Reorganize UltiSnips snippets

[Alex George]

Apparently UltiSnips is rather flexible in how it looks for snippets:

Using a strategy similar to how Vim detects |ftplugins|, UltiSnips iterates
over the snippet definition directories looking for files with names of the
following patterns: ft.snippets, ft_*.snippets, or ft/*, where "ft" is the
'filetype' of the current document and "*" is a shell-like wildcard matching
any string including the empty string. The following table shows some typical
snippet filenames and their associated filetype.

    snippet filename         filetype
    ruby.snippets            ruby
    perl.snippets            perl
    c.snippets               c
    c_my.snippets            c
    c/a                      c
    c/b.snippets             c
    all.snippets             *all
    all/a.snippets           *all

It would be a good idea to follow the <ft>/<specfics>.snippets format, especially for sets like Perl where I've made several categories of snippets. For example, I could expand them as such:

UltiSnips
` Perl
  ` base.snippets
  ` moose.snippets
  ` idioms.snippets