Save mapping and init from mapping

[jennyfothergill]

Summary:

• add save_mapping function (this required changing the mapping keys to be json serializable (not tuple))

• allow a CG_Compound to be initialized from bead specification or a mapping

• add allow_overlap to decide if ring structures share atoms

• add unit tests

fixes #11 fixes #12

[codecov]

Codecov Report

Merging #14 (682d18e) into master (341a53b) will increase coverage by 0.79%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   96.90%   97.70%   +0.79%     
==========================================
  Files           4        4              
  Lines         194      218      +24     
==========================================
+ Hits          188      213      +25     
+ Misses          6        5       -1     

Impacted Files	Coverage Δ
grits/coarsegrain.py	96.15% <100.00%> (+1.09%)	⬆️
grits/finegrain.py	98.38% <100.00%> (+1.66%)	⬆️

[chrisjonesBSU]

Giving this a try right now. I did get this error message after running pip install -e . in the repo.

Collecting openbabel
  Downloading openbabel-3.1.1.1.tar.gz (82 kB)
ERROR: Could not find a version that satisfies the requirement rdkit (from grits) (from versions: none)
ERROR: No matching distribution found for rdkit