Add informative errors to the R script

[evanbiederstedt]

One day, someone should at least add more informative errors to this script. The first step is a few message() statements which detail what part of the script is being run; that is useful for debugging.

It would also be nice to write a few informative checks. If there's something wrong with the BAM or HLA inputs, throw an error which makes sense.

At the moment, this is somewhat of a backburner issue.

[evanbiederstedt]

I tried to do this for plotting. Naturally, it would be better for someone to write a tryCatch at each step of this script.

One day someone could do that.

[evanbiederstedt]

Somewhat addressed here and here: https://github.com/mskcc/lohhla/pull/5 https://github.com/mskcc/lohhla/pull/6