refactored to comply with Go 1.0. Mainly throwing out container/vector,
switching use of os.error to errors package and random small changes.
Modified some tests.
gofmt
minor fix resolving attributes to ensure that the output is
deterministic. Attributes are now output in the order they were
encountered in the haml source. Tests updated accordingly to not
take into account alternative representations.
Add license file. Ignore generated y.go file.