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
Round to the nearest point when doing layout calculations
Merge remote-tracking branch 'upstream/master'
Merge pull request #155 from ahmeij/master

Add identifier to constraints
Merge branch 'master' of github.com:jvonkluck/teacup into jvonkluck-master
remove 'controller' method and use inline code
Merge branch 'master' of github.com:rubymotion/teacup
Merge branch 'master' of github.com:atomicobject/teacup into atomicobject-master

Conflicts:
	lib/teacup/calculations.rb
Merge branch 'extending-constraints' of github.com:alexrothenberg/teacup into alexrothenberg-extending-constraints
added specs for Symbol-based constraints
version 2.2.0 - thanks to everyone who contribute the new features!
having the constraints in a separate method makes no difference
fixes child view controllers
stupid twitter