Release a new version on vim.org

[SidOfc]

There are some notable changes in master which folks from vimscripts do not yet have access to.

• [x] update doc/mkdx.txt to reflect all new changes since 1.9.1
• [x] add new contributors to honorable mentions (@samarulmeu, @victorkristof)
• [x] implement #100
• [x] implement #101
• [x] implement #103
• [x] release on vimscripts