Adding Seq#reverse
Updating roadmap
Writing jdoc for Col
Minor cleaning in Reducible
Reworked Builder interface and SeqBuilder

Builder has been modified to be an independent interface of Col. It's
status as a mutable entity has been made clearer. The new builder
interface exposes basically only one method: add() + variations on
add(). SeqBuilder has been turned into an interface adding cons() on
top of Builder. ListBuilder has been modified to implement this new
interface. As part of the changes to ListBuilder, EmptySeqBuilder
became superfluous and is now gone. EmptySeq is now hidden inside
List as a private static class. As such, all implementation details
of List are gathered inside List.java and private to this file.
Fixing invalid EmptySeq refs in Seq
Updating jdoc in Col
Adding jdoc to Builder interface