Recompile pk_cpp if outdated

[kennykos]

Closes #234

[IvanGrigorik]

@kennykos can you add some unit test to verify the correctness?

[gliga]

We should not use timestamps to check if something is new(er). We should use hashes of files/directories.

[kennykos]

We should not use timestamps to check if something is new(er). We should use hashes of files/directories.

The most recent commit checks the compiled functor.hpp file directly.

[kennykos]

@kennykos can you add some unit test to verify the correctness?

I'm not sure how to write unit tests for this without using exec as it involves files being changed. Do you have any ideas?

[IvanGrigorik]

@kennykos can you add some unit test to verify the correctness?

I'm not sure how to write unit tests for this without using exec as it involves files being changed. Do you have any ideas?

It would be enough to test is_current directly, not whole app.
But if you want to check the whole app - you can append one char of file during tests and do 3 exec rounds in a loop or something like that