Using kcal/mol and ang; added tests for conversions and base units

[chrisjonesBSU]

In a previous PR I changed some of the temperature conversion functions to use kcal/mol and ang_to_m as they should be, but I forgot to add these to base_units.py. This PR fixes that issue as well as creating some unit tests for the functions in unit_conversion.py as well as a double-check of the conversion factors used in base_units.py

[codecov[bot]]

Codecov Report

Merging #40 (d7cead6) into master (a294d56) will increase coverage by 4.42%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   82.87%   87.30%   +4.42%     
==========================================
  Files           6        6              
  Lines         438      441       +3     
==========================================
+ Hits          363      385      +22     
+ Misses         75       56      -19     

Impacted Files	Coverage Δ
uli_init/utils/unit_conversions.py	100.00% <ø> (+100.00%)	:arrow_up:
uli_init/utils/base_units.py	100.00% <100.00%> (ø)