PG Tips

Creates a dictionary of filenames for each event. For example, suppose we
have the following list of files:

    .000.cursormoved.vimhook
    .123.bufwritepost.vimhook
    .SHOULD.MATCH.vimhook
    .bufwritepost.vimhook
    .cursorhold.vimhook
    .foo.cursorhold.vimhook
    .something.else
    should.not.match.vimhook
    a-regular-file.txt

The FindHookFiles function will create a dictionary that looks like the
following (note that "match" is not a valid Vim autocmd event name, but
whatever, it'll just never get used):

    {
        'cursormoved': [
            '.000.cursormoved.vimhook'
        ],
        'bufwritepost': [
            '.123.bufwritepost.vimhook',
            '.bufwritepost.vimhook'
        ],
        'match': [
            '.SHOULD.MATCH.vimhook'
        ]
        'cursorhold': [
            '.cursorhold.vimhook',
            '.foo.cursorhold.vimhook'
        ]
    }