revamp SequentialRoomsUndirected & SequentialRoomsDirected

[Sid-Bhatia-0]

1. Remove old SequentialRoomsUndirected and SequentialRoomsDirected.
2. Add new SequentialRoomsUndirectedModule.SequentialRoomsUndirected and SequentialRoomsDirectedModule.SequentialRoomsDirected with improved implementation.
3. Add agent_direction information to RLBase.state for directed environments when state style is InternalState.
4. Fix and update tests. Execute RLBase.state inside tests.
5. Update README.

Here is how the new environments look:

SequentialRoomsUndirectedModule.SequentialRoomsUndirected:

SequentialRoomsDirectedModule.SequentialRoomsDirected:

[codecov-commenter]

Codecov Report

Merging #155 (7fbad43) into master (f5a27bf) will decrease coverage by 1.40%. The diff coverage is 76.40%.

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
- Coverage   73.24%   71.84%   -1.41%     
==========================================
  Files          25       26       +1     
  Lines        2396     2472      +76     
==========================================
+ Hits         1755     1776      +21     
- Misses        641      696      +55     

Impacted Files	Coverage Δ
src/envs/envs.jl	72.72% <ø> (-21.03%)	:arrow_down:
src/envs/sequential_rooms_directed.jl	57.14% <57.14%> (ø)
src/envs/sequential_rooms_undirected.jl	82.14% <82.14%> (ø)
src/rlbase.jl	82.69% <88.88%> (+24.35%)	:arrow_up:
src/grid_world_base.jl	25.64% <0.00%> (-1.29%)	:arrow_down:

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