Initial commit
Added code to convert Python functions to OCL.

- It's almost working, I think
Can now convert Python to OCL!
Got AST conversion test working again
Fixed some errors with AST code generation.

- Now supports closure variables
- Fixed problem with lambda functions in function_map
Fixes to probes, so we now pass more Nengo tests.
Fixed bug where python function arguments overwrote.
Added newline to end of gitignore
Made test_ast_conversion work again
Made AST conversion better.
Got more functions working with AST
adding support for lambda functions

- and tests for numpy and math functions

- rounding 2nd arg for math.pow test
  (it does not like negatives raised to non-integers)
Got all ast conversion tests passing

- @bptripp's lambda function code is now fully integrated
  with my additions
Changed copied to get, like model.get

- This simplified some example syntax
AST conversion now supports vector inputs.

- I also added support for very basic list comprehensions
Fixed bug with sign function on GPU
AST conversion now supports simplification
Now uses nengo.builder.Builder

- Also changes due to refactoring in Nengo PR #177
- TestSimulator is now explicitly imported, as not all simulators
  are expected to pass these tests (but these are valid for
  the OpenCL backend, for now)
- Also fixes a lif_rate bug due to recent LIF changes
Fixes for changes to Signals

- See Nengo PR#183
Changed length ValueError to assert

- sim_ocl caught the AssertionError but not the
  ValueError, so I figured that's what it should have been.