adjoint 4pi convolution and interpolation

[mreineck]

Implement code which performs the adjoint operation of what's done in #12. While not necessary for time stream generation, it is an important ingredient in deconvolution map mapmaking.

[mreineck]

The basic code is there, but adjointness tests fail. I'm debugging this.

[mreineck]

Adjointness is fixed. The adjoint convolution code is not yet properly parallelized, but that is an easier task than ensuring correctness.

If someone would like to validate the code, feel free!

[ziotom78]

Hi @mreineck , I am not an expert of the mathematics behind convolutions, but I downloaded your code and compiled it: everything worked as expected, and pytest ran 8 tests successfully.

[mreineck]

Thanks!

For the next steps, I'll simply provide the triple of convolved values for T, G and C separately. Even if this is not exactly what's required, I'm confident that the necessary quantities can be computed from this triple; and in the longer term I'll of course adjust the code if needed.