Major API changes

[gucio321]

introduce the following refactors:

• change pkg/players/player.Player type into interface (GetMove and String)
• introduce above change to pkg/players.Players
• add pkg/core/pcplayer.PCPlayer type
• add player.Player impl in pkg/core/pcplayer.PCPlayer
• add pkg/game.humanPlayer implementation of player.Player interface
• mov player.PlayerType into game.PlayerType
• introduce changes above in both: giu and terminal implementations of the game

[codecov]

Codecov Report

Merging #176 (d1ba275) into master (5301c39) will decrease coverage by 0.77%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
- Coverage   96.10%   95.32%   -0.78%     
==========================================
  Files           6        5       -1     
  Lines         359      342      -17     
==========================================
- Hits          345      326      -19     
- Misses         13       15       +2     
  Partials        1        1              

Impacted Files	Coverage Δ
pkg/core/pcplayer/pc_player_engine.go	97.97% <96.66%> (-2.03%)	⬇️

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