Implemented parsing Roman Numerals

[AmPhIbIaN26]

So the parse_number() now works like this:

>>>parse_number('MMCDXX')
'2420'

And parse() works like this:

>>> parse('Built in MDCCLXXVI', language='rom')
'Built in 1776'

[codecov]

Codecov Report

Merging #63 (4c127ec) into master (c834854) will decrease coverage by 2.03%.
The diff coverage is 36.36%.

@@            Coverage Diff             @@
##           master      #63      +/-   ##
==========================================
- Coverage   98.78%   96.74%   -2.04%     
==========================================
  Files          86       87       +1     
  Lines         328      338      +10     
  Branches       60       64       +4     
==========================================
+ Hits          324      327       +3     
- Misses          1        7       +6     
- Partials        3        4       +1     

Impacted Files	Coverage Δ
number_parser/parser.py	95.63% <30.00%> (-2.72%)	⬇️
number_parser/data/rom.py	100.00% <100.00%> (ø)