Revert "travis: install ruby-ronn"

This reverts commit 822a6f8e069b7accf622004465b521900cc5357e.
Makefile: move man target as an install dependency

The ruby-ronn dependency for the man page generation should not be a
dependency to compile i3blocks. So add the "man" target as a dependency
for "install" instead.
scripts: (volume) handle clicks and mute

Thanks to:
  @xelite for mouse volume controls
  @jpleau for feedback about UI design
  @Elfram for mute display
  @Nycroth & @vivien for converting the ruby filter to perl

[vd: fix whitespace and remove the ? char from the regex]

Closes #46, #47, #48, #49, #51
sched: fix unexpected exit when hiding the bar

When the bar visibility is toggled (e.g. with "i3-msg bar mode toggle"),
sigwaitinfo may be interrupted and causes i3blocks to quit.

To avoid this situation, silently continue on EINTR.

In the meantime, display the corresponding errno message when
sigwaitinfo fails.

Fixes #54