add contour.setStartPoint + test

[typemytype]

see #639

[codecov[bot]]

Codecov Report

Merging #668 (ee6e609) into master (54366d9) will decrease coverage by 0.06%. The diff coverage is 57.89%.

@@            Coverage Diff             @@
##           master     #668      +/-   ##
==========================================
- Coverage   77.91%   77.85%   -0.07%     
==========================================
  Files          41       41              
  Lines        6081     6100      +19     
  Branches     1065     1071       +6     
==========================================
+ Hits         4738     4749      +11     
- Misses       1142     1146       +4     
- Partials      201      205       +4     

Impacted Files	Coverage Δ
Lib/fontParts/base/contour.py	55.12% <57.89%> (+0.10%)	:arrow_up:

[benkiel]

Closes #639