Implement On-Balance Volume (OBV) Strategy. Fixes #342

[cinar]

Describe Request

Implements the On-Balance Volume (OBV) trading strategy using the existing volume.Obv indicator.

This PR also includes:

• A fix for a calculation bug in the OBV indicator where it was comparing the current closing price to the previous OBV value instead of the previous closing price.
• Updated test data for the OBV indicator.
• 100% test coverage for the new strategy.
• Updated documentation.

Fixed #342

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.13%. Comparing base (2f2e411) to head (b990cbb).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #355      +/-   ##
==========================================
+ Coverage   93.06%   93.13%   +0.07%     
==========================================
  Files         214      215       +1     
  Lines        6127     6190      +63     
==========================================
+ Hits         5702     5765      +63     
  Misses        344      344              
  Partials       81       81              

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