start to implement unimplemented builtins, but only throw the NotImplemented error.  This is better than a NameError.
Merge pull request #75 from rixner/master

Cleanup after pull request #72.
Merge pull request #76 from rixner/master

Optional arguments for string methods.
Add all unimplemented builtin functions to builtindict, and give them a simple implementation in builtins that just throws an exception.  This is better than NameError.
Merge branch 'refs/heads/builtin-cleanup'
Add placeholders for all unimplemented builtin functions.  Have the stub simply throw a NotImplemented exception.
Failing test
Implementation of map, filter and reduce
Merge pull request #80 from albertjan/map-filter-reduce

Implements map filter reduce
Fixes to make closure compiler happy.