Refactoring code structure

[d-jo]

Currently the src/lib.rs file is empty, and that file should contain the library logic. The types can stay separated, but the querying should be moved to a src/lib.rs

This change is pretty important for tests, as the methods will be able to be accessed easily.

[d-jo]

On second thought, the structs could be merged into a single file as well, maybe src/types.rs? The src directory would contain lib.rs types.rs

I've prepared a branch that does what I am proposing, it still contains a main file but that will change after integration tests are started.

Once #15 is accepted I will submit a PR.