Implement emptyOrSingleton
Refine last in inheritance tests
Implement Iterable.last
Optimize Range for Integers
Implement forKey()() and forItem()()
Fix SequenceBuilder.appendAll

This method was still considering that the parameter was an
ArraySequence when it is really an Iterable
Default implementations of List withLeading/withTrailing

These are concrete implementations. Subclasses must refine them with an
optimal implementation depending on their internal representation.
Implement List withLeading/withTrailing
minor improvement of generated code
Add sum() function
withLeading/withTrailing are now actual so no need to refine them
export ContainerWithFirstElement
tabs -> spaces
Implement ChainedIterator and Iterable.chain
Refine Singleton.equals/count/sorted/contains
Refine Empty.chain/withLeading/withTrailing
Merge remote-tracking branch 'origin/master'
export ContainerWithFirstElement
Merge branch 'master' of github.com:ceylon/ceylon-js
implement ChainedIterator and Iterable.chain