Fix style issues using Rubocop.

This patch fixes about 350 style issues brought to my
attention by using Rubocop [0] for the first time.
Although I don't fully agree with all the style conventions
established in the Ruby style guide [1], this has revealed
at least 2 potential bugs in the code.

Set max line length to 120 though (we have widescreen monitors
these days) and eased some of the code complexity (max lines
per method) checks.

The remaining Rubocop issues are either long lines due to long
string literals and some complaining about class variables in
Command, which are not easily to be exchanged with class instance
variables.

[0] https://github.com/bbatsov/rubocop/
[1] https://github.com/bbatsov/ruby-style-guide
Bump to 0.4.6.
Merge branch 'release/0.4.6' into develop