[cudamapper] Add create_overlapper function to instantiate overlapper object

[nvvishanthi]

Expose instantiation of overlapper object through a create_overlapper() function in the public API and replace the Overlapper creation in main.cu with public API function call.

closes #509

[nvvishanthi]

@mimaric this seemed easy enough to do, so I just added it real quick :). Re-ran the main cudamapper binary on a couple of datasets, and behavior is the same with/without the change. Does this meet the criteria for #509?

[mimaric]

Regarding failing gpuCI/clara-genomics-analysis/check-style test, you can locally run make check-format to check format or just make format in order to automatically correct formatting. If you decide to use make format directly I suggest staging your changes first in order to be able to see the formatting changes so you can learn the rules better

[nvvishanthi]

Looks good to me, just remove #include "overlapper_triggered.hpp" from line 40 in main.cu

Ah good catch. Fixed.

make format fixed the formatting and make check-format is passing on my machine