bgzipped human ancestor FASTAs for samtools 1.x

Konrad;
Thanks much for LOFTEE. We integrated it into bcbio's VEP support and have been using it on a couple of projects locally. It's a great resource.

When using it recently we realized that new samtools 1.x doesn't support/provide anything for razipped files and now uses bgzipped indexed FASTA files. We'd also been having issues with samtools intermittently having trouble reading the indexes for unexplained reasons (https://github.com/chapmanb/bcbio-nextgen/issues/468).

To fix both those problems I prepped bgzipped and indexed files here. This patch adds them into the readme but feel free to grab them into your own download or whatever works best. Thanks again.