Add an external configuration variable Sk.inputfun.  This can be configured similar to the Sk.read variable for importing files.  It is backward compatible with the current practice of using prompt.
Implement use of keyword arguments for __init__ methods.
Pass through all argument types to klass, so they will work correctly
with __init__ if they are implemented later.
Fix type built-in function output to use 'type' or 'class' correctly.
Make isinstance throw TypeErrors like Python for invalid arguments.
Add sk$type to enable type checking on classes.

Rename $is_klass to be sk$klass.
rebuild skulpt
bug fixes to urllib.request plus a test page.
Merge branch 'master' of https://github.com/bnmnetp/skulpt