Add initial Objective-C implementations of Ruby Enumerable mixin.

* This includes collect (map), detect (find), select, reject, and inject (reduce).
Expose simplified NSObject (TWTEnumerable). Add support for enumerators.
Change Enumerable into class + protocol + informal protocol.
Rename everything and hide the enumerator interface.
deprecated TWTSimpleMap in favor of twt_collectWithBlock:
renamed to TWTBlockEnumeration
fixed bug in select method and added tests for NSArray implementations of enumeration methods
fixed error message
updated collect test to test all types of collection tests
added one to random in case of zero
updated collection test to remove string test
added tests for dictionary enumerations and fixed bug in twt_detect when dealing with dictionaries
added documentation for block enumeration
updated for pull request comments, refactored duplicate definitions into a protocol, updated readme
Merge branch 'master' into enumerable
updated podspec
clean up on block comments
improved test for CI failures
fixed broken test on CI. Updated yml to support UTF-8
updated documentation per further notes