Include hg38 setup

[roryk]

Heya!

RepEnrich has hg38 indices built but RepEnrich2 only has hg19. I built the hg38 indices using the hg38_repeatmasker_clean.txt file from RepEnrich1 using the setup script from RepEnrich2. I stuck them up on Dropbox RepEnrich2_setup_hg38.tar.gz if you want to grab them and add them to your Google Drive with the other indices.

I also made several quality of life improvements for RepEnrich2_setup.py, including the ability to pick up where you left off in case of a failure. I saw in the RepEnrich repository that there are some useful pull requests that never got addressed. Do you all accept pull requests?