Introcs

* Added experimental `modlib` module (unexposed)
* Reverted to wheel over egg

* `testcase` functions now support custom error messages
* `geom` package refactored to minimize `numpy` (to prevent memory crash in Python Tutor)

* Added unverified context to fix problem with `SSLContext`

* Added `SSLContext` support to connect to https://
* Fixed another race condition in `turtle` package

* Another attempt to fix race condition in `turtle` package

* Fixed problem in web color parsing
* Fixed race condition in `turtle` package