Rename Cequel::Model -> Cequel::Record

Makes the use of the Active Record pattern more explicit
Cequel::Record mixin for models

No more Cequel::Model::Base

Step for #40
Move most everything out of Cequel::Record module

It's just a meta-mixin.
Move schema definition into Schema module
Update README
Merge pull request #40 from cequel/cequel-record

Cequel::Record