brentp/vcfanno: multiple alts, multiple lines, overwrite.

v0.2.7 (dev) restore multiple threads per annotation file after fix in biogo/hts (#64) add setid builtin to set the ID field and remove need for lua and fix some bugs. fix bug in self with multiple alternates when there were multiple overlaps (thanks Matthew). fix for #68, #69 -- with Number=A, op="self", the output will always have a number of elements equal to the number of alternates. If there are > 1 annos for a given site, later values will overwrite previous