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.
Since the class is private, could it either be indicated so in the name or be made a member class of `ESearch`? I think it may also be possible to remove this object in favor of a `namedtuple`