Refactor orch/__init__.py and main wscript file

[brettviren]

Right now the orch/init.py file does too many things.

• parse config files
• recur build() into any override /wscript
• bind functions to the Context

At the very least, the recursion should be moved into the top-level wscript file.

It's probably good to move this out of init.py so it's easier to import orch submodules for unit tests.

[brettviren]

This has been done. orch.waffuncs now holds this functionality.