ADD lib.py to make argnorm usable as a library

[Vedanth-Ramji]

Making argNorm better suited as a library.

• Providing a separate map_to_aro function so argNorm can be used without the normalizers
• Separated get_aro_mapping_table function from BaseNormalizer so it can be used independently

[luispedro]

I'm not sure about splitting to general. Is the goal that people import it as

from argnorm import general

?

Also, tests are needed

[Vedanth-Ramji]

Yes, well now that I have renamed it to 'lib' it should be something like: from argnorm import lib or from argnorm.lib import *.

Is that ok?

[luispedro]

Can you some notes to the Changelog about this?