Chicago issue smash

On my travels to (and from) the excellent [Windy City Rails](http://www.windycityrails.org) in Chicago a few weeks ago, I took the time to address a bunch of issues here is the CHANGELOG broken down;

* Fix plugin config issues with user input (#225 #223)
* Fix Linux FPS timing issues (#215)
* Fix hook enable/disable issue (#206)
* Fix Git GUI issues (#196 #168 #193 #188 #159 #133 #123 #119 #104 #83)
* Mention Boxen script in README (#208)
* Explain global Git hooks how-to in README (#212 #112)

Also made some minor improvments to Linux Capturer class (the `--debug` was failing there).  Hopefully (thanks to the suggestion by @florianbachmann in #196) all GUI client issues should be solved.  

A combination of 2 path problems seemed to be the main issue (both Ruby and ImageMagick need to be in the path!).  A previous fix for we applied (for Ruby) had been incorrect.  I have tested all GUI clients mentioned in the related issues and they now all work (and capture) fine for me.
Actually, i'll keep it in the CHANGELOG, since its missing here, and will be included in the next release.