Convert Changes.rst to keepachangelog style

[stephenrauch]

• [x] tests added / passed
• [x] passes tox

• Convert Changes.rst to keepachangelog style
• Cleanup is_address()

[codecov-commenter]

Codecov Report

Merging #119 (7646675) into master (d334816) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #119   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        15           
  Lines         3254      3254           
  Branches       788       788           
=========================================
  Hits          3254      3254           

Impacted Files	Coverage Δ
src/pycel/excelutil.py	100.00% <ø> (ø)
src/pycel/excelwrapper.py	100.00% <100.00%> (ø)
src/pycel/version.py	100.00% <100.00%> (ø)

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