Fix travis url in README.md
Merge fn and lambda

We actually only generate an ast.Lambda if (lambda) was called, as a lot of code
expect ast.FunctionDefs (most notably with_decorator).

This allows empty lambdas too.

This fixes #165.
Add a test for lambda w/ lambda-list
Implements defclass

This fixes issue #156

Signed-off-by: Julien Danjou <julien@danjou.info>