Fix quote in markdown-mode-font-lock-keywords-gfm
Added `markdown-insert-item-list`. When at the end of line, this will insert bullet/number on the following line. With prefix arg ascend/descend a level.
Fix `markdown--cleanup-list-numbers-level` freezing at the end of buffer
Merge pull request #3 from Fuco1/addlist

Added markdown-insert-list-item