Elder Ray Strategy added. Issue 343

[whencanibe]

Describe Request

Implements the Elder Ray Strategy as requested in issue #343

The Elder Ray indicator already exists in the momentum package.
This PR adds the strategy layer on top of it, following the existing patterns in strategy/momentum.

Fixed #343

Change Type

New strategy.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.02%. Comparing base (2db1c9a) to head (5ab2ff9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #385      +/-   ##
==========================================
+ Coverage   93.97%   94.02%   +0.04%     
==========================================
  Files         224      225       +1     
  Lines        6477     6530      +53     
==========================================
+ Hits         6087     6140      +53     
  Misses        309      309              
  Partials       81       81              

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[cinar]

Thank you for your contribution!