Omega: Missing support for newer weighting schemes

[Vivek Pal]

Hi,

In my explorations of Omega codebase, I have found that Omega is currently
missing support for newer weighting schemes added in 1.4.1 (BM25+, PL2+,
Dir+). I'd submit a PR addressing that but as I think I might be missing
something so just wanted to check if there's a particular reason for that?

P.S. Finally back after a long week. Been eagerly waiting for a weekend since
the application period ended. (last month of each semester has always been
engaging actually).

Thanks,
Vivek