Revamp icons

Add support for highlighted icons
Add non-retina versions for all icons
Add new icons for tag, fetch, pull, push, detail and tree
Add icons for collapsed and expanded folder items
Refine colors for file icons
Rename Images.pxm to Icons.pxm
Pixel-align html action icons
Pixel align hires icons and buttons
Pixel align icons and buttons
Correct pixel aligned buttons
Log errors from gistie's xhr exchange

Previously would only show errors with HTTP 2xx responses
Update PBWebHistoryController for GTConfiguration
Update gisting to the v3 API

v1 & v2 have been dead for quite a while
Use the Personal API Access Token when posting gists

Can be created at https://github.com/settings/applications, then set with "git config --global github.token bef91b559df0014f71c212fc44171b5bc6de12e9a"
Save the files that are missing from the SyntaxHighlighter repo upstream
Update help link to GitX fork website
Uptate objective-git install instructions

- update_libgit2 was renamed without .sh extension
- update_libgit2 script must be run in the objective-git folder
Add details about GitX-dev fork in About menu

- Add fork name & tag line
- Update link to current github.io domain
Merge branch 'refs/heads/master' into issues/204
Add pull request #204 to the change log
Merge branch 'issues/204'
Merge branch 'refs/heads/master' into issues/206
Add pull request #206 to the change log
Just show Pieter's name in the copyright string
Merge branch 'issues/206'