* references: add ALEFindReferences -fzf option
Allows using -fzf to show previews using fzf.vim. Includes:
- add support for opening in bufers, splits, tabs and for adding matches quickfix
- add support for -relative
- add fzf preview `--highlight-line` option
- add fzf.vim autoload module
* tests: fix references tests for fzf support update
