lib/mnit: rewrite doc of `InputEvent`

In response to issue #242.

<Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/mnit: rewrite doc of `input_events`

In response to issue #241.

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge remote-tracking branch 'alexis/mnit-comments'

in response to #241 and #242