Namespace pollution

[alecloudenback]

There's a lot of very short characters exported by the module, which pollutes the user's namespace. Some solutions:

1. Don't export anything and require explicit import
2. alias some of the basic functions e.g. insurance for A and export the aliases
3. Keep as is

I'm leaning towards option 2 as the best use case for most people.

[alecloudenback]

v was changed to disc in #19

[alecloudenback]

Current Plan:

Keep the shortened version, but unexported. Export the following:

• ä -> annuity_due
• a -> annuity_immediate
• A -> insurance ?
• P -> premium_net
• V -> reserve_premium_net

Don't export the Commutations, but keep their single-letter designations.