Merge pull request #21 from lyokha/master

fixed processing of long options with equal sign
Merge pull request #24 from lyokha/master

fix for issue #23 in upstream
Implement suggestion by @lyokha on issue #23

We switch folding methods when changing into and out insert mode, so
MarkdownFoldExpr is not used when typing.
some tweaks to folding module.

reduce number of calls to getline() in main and texttile foldexpr
functions
limit some lookbehinds
Change header mark in foldtext.

closes issue #25.
changes header mark for textile.
Make the folding method be configurable on a per-buffer basis.
fixes in folding

Comments to all chunks:

1. A typo: extra parenthesis breaks all folding
2. There is no need for look-behind here because '^' is zero-width and
   len(matchstr(...)) will be same whereas matchstr(...) will trigger
   same way. (i already omitted such look-behind in MarkdownLevelSA())
3. There could be 6 '#' and one space: 7 bytes altogether