Add a module to support DRF operations

[rneswold]

acsys needs a module which understands DRF. There have already been a couple issues (#8, #14) which could be solved or supported if we could parse DRF strings.

This module could:

• Parse DRF strings into the various components
• Add a class hierarchy which models DRF requests. These classes' .__str__() method would return DRF strings.

[beauremus]

This is a good use case for a service 😉
We should have a reference implementation that other applications can make queries to.
Reimplementing this in Python could lead to inconsistencies.

[rneswold]

If it becomes a service:

• We can use protocol compiler to model DRF.
• DRF parsing will be slightly slower than native parsing, but everyone gets the same support.

If we add a parser to acsys.drf:

• We need to create a set of DRF examples that all implementations need to successfully parse.
• We need a document that identifies all parsers so their maintainers can be notified when DRF changes (for instance, only Charlie's Java parser supports some DRFv3 features that no other parser supports.)