Misc fixups
Keyword search over all document fields

* Extract query building from search repository
* Add text search capability
Assignment rather than merging and simplify return

- Use words rather than letters for itterator variables
- Use assignment rather than merging two hashes
- Array plus blank is the same as array so just return rather than
  checking for blank status
Merge pull request #15 from alphagov/keyword-search

Keyword search