The Context.Label method and LABEL global function did not agree. Also
breaks the convention I'd like to set that capitalized functions must
agree with existing Go assembly syntax.
To help avoid a conflict with `avo.Label`, attributes were moved to
their own package.
Fixes#35
Previously GLOBL/DATA attributes are set to RODATA. This diff removes
that default and allows them to be set through the DataAttributes
context method.
Updates #2
