A fresh, asynchronous start. Add Clock
Add more asynchronous tasky goodness
Add our very own Futures

They're tied to a clock!
Fix test of recursive advance()
Use `delay` instead of `dt` where it makes sense
Yielding "None" sleeps for 0 units
Add Expression and Constant
Add a settable Value expression
Add __repr__ to Expressions
Add +, -, *, / operators to expressions
Add rudimentary constant propagation
Improve pep8 compliance
Allow Value to be "fixed"
Add a duplicate-friendly dump function
Add negative tests for commbining expressions of different len()s
Add expression slices
Slightly more aggressive simplification
Add a Concat expression
Add a replace() method
Improve handling zero-length expressions