Release 0.10.0

API-Incompatible Changes

• Drop support for Python 3.4.

API Additions

• AssertRaisesContext and AssertWarnsContext now return themselves
  when __enter__() is called. By extension it now easier to call
  add_test() with assert_raises() et al:

with assert_raises(KeyError) as context:
    context.add_test(...)
    ...

• Add AssertRaisesContext.exc_val property to access the caught
  exception after leaving the context manager:

with assert_raises(KeyError) as context:
    ...
assert_equal("expected message", str(context.exc_val))