enhance next/prev follow link
use regexp and pattern order
update default prev/next pref
update comments and shorten code
Merge branch 'enhance-follow-link' of https://github.com/zhuochun/VimFx into zhuochun-enhance-follow-link
Refactor follow prev/next links

- Simplified everything.
- Made it more DRY.
- Patterns can include the * and ! wildcards, just like the black list.
- Patterns must match either at the beginning or at the end of the link
  text.
- Patterns don’t match in the middle of words. Works with non-English
  characters too.
Merge pull request #264 from lydell/zhuochun-enhance-follow-link

Refactor follow prev/next links (supersedes #260)