Initial commit
Update README.md
Test commit
First real commit.  Add a basic event library

Currently only supports I/O events, no events on a timer. Also includes a basic test, and a super simple 'test framework' for adding further tests.
Add disclaimer to test_event.c
Add 'poll' event implementation.  Fix a nasty bug in event.c.

Nasty bug: adding a callback to an existing io_event but for a different state overwrote any callbacks you'd already registered! Bad.