Add enums for player fields

[andrewsayre]

Description:

New

HeosPlayer

• New control property to indicate the volume control type when lineout is Fixed.
• lineout is now an enum of type LineOutLevelType

types module

• Added LineOutLevelType and VolumeControlType

Related issue (if applicable): closes: #72

Checklist:

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Tests have been added/updated. No exclusions in .coveragerc permitted.
• README.MD updated (if necessary)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.76%. Comparing base (5de8286) to head (063cfac).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev      #73   +/-   ##
=======================================
  Coverage   99.76%   99.76%           
=======================================
  Files          19       19           
  Lines        2108     2114    +6     
=======================================
+ Hits         2103     2109    +6     
  Misses          5        5           

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