Support bgzip fasta file

[timoast]

Hi,

Thanks for the great tool! I ran into an issue recently when trying to use a bgzip-compressed genome FASTA file as input, the program would crash every time. Looking at the crash report pointed me to lines in the FASTA reader and I eventually worked out that the FASTA needs to be decompressed for it to work.

Would it be possible to support bgzipped FASTA, or if not maybe add a check to make sure the FASTA file is not compressed?