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>
Run unit tests against hy2py

Signed-off-by: Julien Danjou <julien@danjou.info>
Fixup comment
Merge branch 'jd/defclass' of https://github.com/jd/hy into jd-jd/defclass
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