Prepare the project for the release

[c71n93]

Fix TODOs

• Add 0pdd to the project and reformat all the TODOs to match 0pdd format.

• Watch through all the TODOs and fix what is possible.

Polish the project architecture

• Make the project modules easier to test. Use the idea of deep modules.

Testing infrastruction

• Add sufficient testing.

• Add a CI.

[0pdd]

@c71n93 2 puzzles #4, #7 are still not solved.

[0pdd]

@c71n93 the puzzle #4 is still not solved; solved: #7.

[0pdd]

@c71n93 3 puzzles #10, #4, #9 are still not solved; solved: #7.

[0pdd]

@c71n93 4 puzzles #10, #11, #4, #9 are still not solved; solved: #7.

[0pdd]

@c71n93 5 puzzles #10, #11, #12, #4, #9 are still not solved; solved: #7.

[0pdd]

@c71n93 5 puzzles #10, #12, #13, #4, #9 are still not solved; solved: #11, #7.