Canonicalise iterator receiver names

This apparently meaningless churn improves godoc readability.
Canonicalise leveldb receiver names

Also remove redundant LevelDB infix missed previously.
Canonicalise memstore receiver names
Canonicalise mongo receiver names

Remove redundant Mongo infixes that were miseed previously.
Canonicalise gremlin receiver names
Canonicalise mql receiver names

And again, remove a multitude of redundant infixes I missed previously.
Remove unnecessary import renaming
Merge pull request #31 from kortschak/names

Rewrite receiver names
Fix build by only testing Go >= v1.2
Merge pull request #32 from barakmich/master

Fix build by only testing Go >= v1.2