Run single variant and aggregation tests only within region

[welchr]

Especially as input files and number of studies gets large, it would be useful if rare metal could use tabix from the results and covariance matrices to select only the parts of the genome it needs for the test instead of loading the entire chromosome/genome. It would make the process less computationally cumbersome or have the benefit of not requiring us to again make many subsets of the initial files for specific analyses that are computationally feasible.

Currently I believe --range chr:start-end works partially for this, though it looks like it may still run the single variant analysis chromosome-wide. Needs further assessment.

Also this parameter appears to be undocumented.

[welchr]

Since docs aren't maintained in this repo, we'll have to edit wiki to include this new "official" parameter.

Usage is: --range chrom:start-end. Single variant tests and group tests are limited to only those within that given range/region.