Added the ability to "inherit" constraints when extending a style

The logic ensures that only one constraint for an attribute will be applied in the new style

It is not perfect:  if you use a symbol in the base style such as `:top_left` and `constraints_top(8)` in the extended style
both will exist incompatibly.
Adding constraint support for topLayoutGuide
Adding iOS 6 friendly support and bottom_layout_guide
Adding iOS 6 friendly support and bottom_layout_guide
Adding helper method to resolve controller without sugarcube dependency and removing explicit self references
Merge remote-tracking branch 'upstream/master'
Adding testing for constraints relative to top_layout_guide and bottom_layout_guide
note about extends accepting an array
added a note about these messages
Updated the readme with the right information to set the bar tint color
Fix issue with setting color for the UIBarButtonItem
Merge pull request #144 from stefanvermaas/master

Updated the readme with the right information to set the bar tint color
use numbers or stylename in 'constrain_size'
some helpful text
more info re: dummy.rb
fix link
Updated the readme, because styling the UINavigationBar has an awful way of setting the title text attributes
Merge pull request #147 from stefanvermaas/master

Updated information about UINavigationBar
prefer 'teacup_subviews' over 'UIView#subviews'
whitespace