sanity checks for sorted and RGs

[hemstrow]

Hey there!

I've noticed some less-than-informative errors when running smoove with bam files not sorted by position files, those without read groups, and particularly with read groups without the SM tag. I don't see anywhere in the documentation that these are required, so figuring. Are sanity checks for these possible?

Thanks!

[brentp]

Hi, I'm happy to accept PRs that improve error messages.