Adhere to PEP8

[sumanthratna]

This commit:

• reduces the number of autopep8 warnings
• adds optional to appropriate named arguments in docstrings
• formats README with Tidy Markdown

Nothing serious, just formatting changes. Feel free to close this if you don't want these changes.

[codecov-io]

Codecov Report

Merging #20 into master will increase coverage by 0.02%. The diff coverage is 76.19%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   96.77%   96.79%   +0.02%     
==========================================
  Files           5        5              
  Lines         155      156       +1     
==========================================
+ Hits          150      151       +1     
  Misses          5        5              

Impacted Files	Coverage Δ
tableprint/printer.py	94.18% <70.58%> (+0.06%)	:arrow_up:
tableprint/utils.py	100.00% <100.00%> (ø)

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[nirum]

Thanks!