Add obstacles tutorial

[blegat]

Taken from Joey Huchette at SIAM Opt 2017

@joehuchette do you still have the code?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.46%. Comparing base (a4e1a6a) to head (47fbe4b).
⚠️ Report is 99 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #257      +/-   ##
==========================================
+ Coverage   78.17%   78.46%   +0.29%     
==========================================
  Files          36       36              
  Lines        1700     1788      +88     
==========================================
+ Hits         1329     1403      +74     
- Misses        371      385      +14     

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