Support old architectures when compiling

[brettolsen]

The "-march=native" option produces compiled code that is optimized for the chip architecture of the build machine. This can produce compiled code that will not run on older chips, instead crashing with "illegal instruction".

In particular, the bioconda compiled package available here (https://github.com/bioconda/bioconda-recipes/tree/master/recipes/moods) apparently is compiled on a Haswell (AVX2) machine, preventing a wide number of users running on older machines from successfully installing MOODS using conda.

[jhkorhonen]

I chose -march=native with the assumption that the code is compiled on the target machine, and any distributors will tweak the compile options to suit their targets. However, based on quick testing, it looks like -march=native is only ~2% faster than -mtune=generic, so it might not be a bad idea to make that a default.

I'll do a bit more testing and merge this if it doesn't look too bad.

[jenzopr]

I can inject a patch and rebuild the bioconda package, if you'd like to use conda @brettolsen?

[jenzopr]

Ah its done already! Great 🎉