revamp GridRoomsUndirected and GridRoomsDirected

[Sid-Bhatia-0]

1. Remove old GridRoomsUndirected and GridRoomsDirected.
2. Add new GridRoomsUndirectedModule.GridRoomsUndirected and GridRoomsDirectedModule.GridRoomsDirected.
3. Rename RLBaseGridWorld to RLBaseEnv.
4. Fix and update README.
5. Update tests.

Here is how the new environments look:

GridRoomsUndirectedModule.GridRoomsUndirected:

GridRoomsDirectedModule.GridRoomsDirected:

[codecov-commenter]

Codecov Report

Merging #154 (f4bee64) into master (c585c20) will decrease coverage by 1.11%.
The diff coverage is 73.03%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
- Coverage   74.35%   73.24%   -1.12%     
==========================================
  Files          24       25       +1     
  Lines        2379     2396      +17     
==========================================
- Hits         1769     1755      -14     
- Misses        610      641      +31     

Impacted Files	Coverage Δ
src/play.jl	0.00% <0.00%> (ø)
src/rlbase.jl	58.33% <57.14%> (-6.38%)	⬇️
src/envs/grid_rooms_directed.jl	71.42% <71.42%> (ø)
src/envs/envs.jl	93.75% <77.77%> (-6.25%)	⬇️
src/envs/grid_rooms_undirected.jl	81.81% <81.81%> (ø)
src/envs/dynamic_obstacles.jl	92.40% <0.00%> (+0.04%)	⬆️

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