Introduce Mapper#call(relation)
Merge branch 'master' into relation-mapping-support
Add Mapper.build
Memoize mapping in attribute set
Always use attribute names

Since axiom will always return tuples with expected keys there is no need to
use tuple_key to fetch values from tuples
Rename Header.coerce => Header.build
Add projection using attributes from header
Extend spec for Mapper#call
Add some docs
Update flay threshold
Merge pull request #4 from rom-rb/relation-mapping-support

Relation mapping support