Add a script to add chr-pos-ref-alt to input files with only rsid

[sgagliano]

For association results with rsID only, add a script to map the variants to chr:bp (b37).

[pjvandehaar]

Approaches:

• a file tabixed by rsid
  • if the rsid-only file is sorted by rsid, we could hold the last tabixed block in a cache (maybe even in a dictionary?)
• a bgzip file sorted by chr-pos with a [hash(rsid) -> bgzip block] index
  • if our rsid-only file is actually sorted by chr-pos (despite not having them), we could hold the last successful bgzip block as a cache.
• a sqlite3 table
  • see /net/snowwhite/home/welchr/projects/dbsnp/make_sqlite_db.py

[pjvandehaar]

(replaces #43)