Support for cheatsheets as manpages

[orenmazor]

@arthurnn:

SUPER experimental, possibly junky screwing around, support for writing cheatsheets in markdown, then being able to load them in manual pages.

disadvantages:

• we end up cashing the roff formats locally on the first time a user runs a cheatsheet
• stack seems a bit dirtier than before
• ugly exec to call man

advantages:

• markdown is easier to write than yaml
• use kramdown, so we'd be able to build cheatsheets into latex, which opens up a whole new world of cheatsheets
• support man pages, which means we can generate all kinds of interesting and complex cheatsheet formats to review in console

I only implemented help.md for now, and there are probably bugs involving the github adapter, etc etc. this is a reference implementation for discussion :)

[hauleth]

There is native version written by me. See #18. I use Redcarpet with custom Renderer and colorize to make cheats more fabulous. Workin' and tested (So far only manually).

[orenmazor]

@hauleth A+++++++!

I was going to go that route but I was so sure that must already exist. I was hoping this PR would reveal that missing link :)

[arthurnn]

@orenmazor , I end-up merging the other markdown transform PR. the one using Redcarpet. Should we close this one than? anything u wanna keep from here?