Changing output paths and bgzipping

[James-S-Santangelo]

Meant to do this as two separate PRs (output directories + bgzipping) but I committed to the wrong branch and decided to role with it rather than resetting.

Closes #5

• Wrote function to bgzip VCF files after they're generated
• Changed CSV generating script to have cyvcf2 read bgzipped files.

Closes #13

• Created separate output directories for SLiM simulations based on parameter combinations
• Changed CSV generating script to recursively load bgzipped VCFs from newly created output directories.

I think it's nicer having separate output directories for two reasons:

1. It's cleaner
2. Parameter combinations that take different lengths of time to run (e.g., N = 10 vs. N = 1000) are more self contained. This avoids functions that rely on file extensions from operating on files created by a different set of simulations when they're being run in parallel.

[aays]

Looks like merging the random seed PR created a conflict above -- whoops. Seems a quick fix though!