* Lower the severity of some of the errors when they are not really
catastrophic.
* Mention Vundle in all messages
* Make some of the messages a little more specific

Closes #579

If then plugin name check fails during the servicing of a interactive
install request, the operation should leave no traces.

Before this change, git cloning or resetting of the origin remote
occurred before checking the name. This change reverses that.

When Running PluginInstall or PluginUpdate with a list of plugins and
some of those have failed name validation, they are returned as empty
dictionaries. Exclude those before checking the size of the list so that
if all given plugin names failed, then the empty list message is shown.

Name duplication is checked so that users don't end up overwriting one
plugin directory with the contents from another plugin that shares a
common name.

However, if the repeated plugin happens to be the same, there will be no
surprises and there is no need to flag this as an error. This needs if
particularly acute due to the fact that we currently don't show, in the
plugin search, which of the resulting plugins are already installed, so a
user might very well attempt to install a plugin they already have.

With this change, instead of seeing an error in this scenario, the user
will see a message indicating the plugin is already installed, and no
additional cloning will be performed.

Fixes #509

Prevent insecure plugin names.

Plugins' names which contain '../', '$HOME', '%h', '..\', etc.
can be dangerous.
Use a sensible whitelist for plugin names and prevent its expansion.

Refactor global variables to autoload variables

The setting of the default values for the autoload variables is moved out of
any function.  One reason being that these settings do not depend on the
argument of the function.  The second being that Vim will source the autoload
script if an undefined autoload variable is referenced and the file is
expected to define the variable (see :help autoload).

All global variables that are not part of the public API (mentioned in the
documentation) are turned into autoload variables.  This is intended to give
all global variables defined by Vundle.vim a common prefix.  The variable
g:default_git_proto is part of the public API and is therefor not changed.
This is the only exception.

Changed:
   g:bundle_dir            -> vundle#bundle_dir
   g:bundles               -> vundle#bundles
   g:updated_bundles       -> vundle#updated_bundles
   g:vundle_lazy_load      -> vundle#lazy_load
   g:vundle_log            -> vundle#log
Unchanged:
   g:default_git_proto

If it was loaded, unload the log buffer before editing it.  Otherwise the
editing command can "hang" if the user has `set hidden`.

This problem was originally discovered with the VundleChangelog command and
the analogous fix was applied in 7d9b10.  See github issue #468 for more.

These variables only occur in one file each.  By making them script local
variables this is "documented" in the code.  At the same time the global
namespace is polluted less.

Changed:
    g:bundle_names          -> s:bundle_names
    g:vundle_last_status    -> s:last_status
    g:vundle_log_file       -> s:log_file
    g:vundle_view           -> s:view

The variable is script local to autoload/vundle/scripts.vim since #468.

The command `silent pedit ...` was causing trouble if the user had `set
hidden`.  Now we `bdelete` the changelog buffer before editing it anew.

Use svg instead of png to get better image quality

Update minirc to Plugin* commands with #begin and #end

Clarify Readme.

- closes #281

Rearranging rtp so that **all** default directories appear first has the
undesired side effect of not allowing plugins to override default syntax
files.

This changeset limits the rearrangement of the rtp to simply making sure
the first directory in the default runtimepath appears first in also in
the runtimepath after Vundle has finished manipulating it.

This should keep the original bugs fixed and should eliminate the
aforementioned undesired side effect.

Fixes #430
Fixes #456

Allow rtp paths with spaces on Windows

Fixes #451
Fixes #453

Suggested by @ikurcubic

Fixes #443

* Fixes 435

So it can be reused.

Fixes #441

If one had this plugin:

Plugin 'foo/bar'

And now switches to another one with the same name:

Plugin 'baz/bar'

Recognise this scenario and replace the old plugin with the new one,
rather than silently assuming they are the same.

Fixes #367 #48 #183 #400

* Add modelines to all code/doc files excluding README.md.  The modeline used is: `" vim: set expandtab sts=2 ts=2 sw=2 tw=78 norl:`
* Rename links with /vundle to /Vundle.vim, seems to confuse some people with redirect.
* Remove duplicates from Quickstart, add example of `name` flag.
* Add link to Tips page by @Lucc .
* Change help maintain vundle link directly to the new one.
* README.md line number links updated.

Note: Users with bundle/vundle need to rename vundle to Vundle.vim to use test files. Vundle will continue to function otherwise.

Fixes #413.
Fixes #438.

It's a duplicate of the PluginSearch command.

Fixes #428

- Complete the code documentation effort started by @lucc
- Remove some judgemental comments ✨
- Remove comments pertaining to things that should be opened as issues
- Boxed ❗

Also add some FIXME markers in places where the code needs more
explanation.

New supported option called 'pinned' for the Plugin command. When set to
1, the plugin is added to rtp but no install/upgrade operation is
performed.

It not only allows vundle to do rtp management of plugins on VCS other
than git, it also allows leaving plugins that had previously been
managed by vundle in the current state, with no further updates.

Fixes #24, #397

Prevents error 150 when user has doc/* in wildignore

Fixes #112