Support rlintro

[findmyway]

1. Add a string representation to TicTacToeEnv
2. Bug fix with DefaultStateStyleEnv.

[codecov-io]

Codecov Report

Merging #119 (6e1cb9a) into master (8141ddb) will increase coverage by 0.70%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #119      +/-   ##
==========================================
+ Coverage   69.04%   69.75%   +0.70%     
==========================================
  Files          31       32       +1     
  Lines        1037     1081      +44     
==========================================
+ Hits          716      754      +38     
- Misses        321      327       +6     

Impacted Files	Coverage Δ
src/environments/wrappers/DefaultStateStyle.jl	77.77% <0.00%> (-22.23%)	⬇️
src/environments/examples/RandomWalk1D.jl	100.00% <100.00%> (+4.00%)	⬆️
src/environments/examples/TicTacToeEnv.jl	91.25% <100.00%> (+0.07%)	⬆️
src/environments/3rd_party/gym.jl	55.84% <0.00%> (ø)
src/environments/3rd_party/atari.jl	64.47% <0.00%> (ø)
src/ReinforcementLearningEnvironments.jl	100.00% <0.00%> (ø)
src/environments/3rd_party/open_spiel.jl	27.63% <0.00%> (ø)
src/environments/wrappers/MaxTimeoutEnv.jl	100.00% <0.00%> (ø)
src/environments/examples/BitFlippingEnv.jl	82.85% <0.00%> (ø)
... and 2 more

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