WIP: GP now takes opt_params argument

[stevetorr]

I decided to grandfather in maxiter and opt_algorithm as arguments because I thought that breaking everybody's scripts would be rude. I do think that they belongs in the opt_params argument so we can add it in later if we want. Perhaps we could include a warning that opt_algorithm and maxiter will be deprecated with V 1.0 and to use opt_params instead if they are passed in as arguments.

Closes #91

[codecov-io]

Codecov Report

Merging #92 into master will increase coverage by 0.06%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
+ Coverage   51.74%   51.81%   +0.06%     
==========================================
  Files          31       31              
  Lines        4791     4802      +11     
==========================================
+ Hits         2479     2488       +9     
- Misses       2312     2314       +2

Impacted Files	Coverage Δ
flare/gp.py	89.04% <77.77%> (-0.4%)	⬇️

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[dmclark17]

This could be a fun place to try out one of Python 3.8's new features! TypedDicts! I actually don't know if this would be a good use case, but if we turned the opt_param_override into a TypedDict then Python's type checker could check the types in the dictionary

I am just looking for use cases of the new features of python so totally unnecessary to actually implement...