First pass of EUtils ⚠️ (not ready for merge) ⚠️

This ports over all the code that we had in cogent.db, I have explicitly left
out the submodules related to RFam and PDB. I've also ported over the super
awesome tutorial that exercises a lot of the functionality in this module.

The few things that I can think of for immediate improvements are:

- Unit Tests
- Organization (there are far too many private functions).

For now I want to see how we are doing in coverage for these modules and make
sure that everything is Kosher.

It would be great if someone could take a pass at it.
Should we be implementing this ourselves? The [requests](http://docs.python-requests.org/en/latest/) module is going to be better, and is pip-installable.