Reduce graph.Iterator method names
Reduce TripleStore interface names
Don't indirect map values

We already have reference behaviour, so this is not necessary.

This change highlighted fairly baroque architecture in mql that deserves
some attention; the use of channels is somewhat confusing.

Also rename LastResult to Result.
Rename TSVal
Rename AddValue
Merge pull request #46 from kortschak/reduction

Reduce the complexity of names and types in graph.{Iterator,TripleStore}