Add ability to exclude files and directories based on wildignore

[maurizi]

No description provided.

[inkarkat]

Note that this requires ctags support for wildcards (which the version 5.8 Windows binary I'm using doesn't have), as 'wildignore' likely has those, too.

A different approach / alternative might be the easytags_auto_disabled (buffer-local or global) flag introduced by my pull request #83. I use a BufRead autocmd to set this for backup file buffers, to avoid that those are included in the tags file when I open them with Vim. (A :UpdateTags won't consider those (regardless of 'wildignore', as the file pattern doesn't match the list of recognized ctags languages.), anyway.)