Simplify terms query

[awead]

Instead of:
({!terms f=discover_access_group_ssim}public) OR ({!terms f=read_access_group_ssim}public)
do something like:
({!terms f=discover_access_group_ssim v=$groups}) OR ({!terms f=read_access_group_ssim v=$groups})&groups=public

kudos to @erikhatcher for pointing this out in #17

[atz]

Interesting. Wouldn't call this simplification, though. In particular because we need the clauses to be atomic since they are aggregated and crudely OR'd together.

[erikhatcher]

Wouldn't call this simplification, however.

It's DRYer though :)