some refactoring

  * modified fold-marking to enable highlighting
  * replaced some of matchlist() by matchstr()
  * changed s:dangling_import() from recursion to loop
fixed multiline-import completion
Merge pull request #18 from ichizok/refactoring

Some refactoring
Merge pull request #19 from ichizok/fix-multiline-import

Fixed multiline-import completion
Fix ghc-mod version detection

Taken from ghcmod-vim