upgrade to md2man 4.0
rename `load` command to `snip` and remove `conv`

The `binman conv` command has been removed; use `md2man-roff` instead.

We no longer require a specific md2man version at runtime; any will do.
Merge branch 'patch'
Merge branch 'major'
Version 4.0.0 (2014-10-26)