Added docs for foreign key chainable methods
Merge pull request #142 from johanneslumpe/patch-1

Added docs for foreign key chainable methods
Added docs for compound primary key
For for incorrect sql (aggregates with columns)
Merge pull request #143 from p-baleine/topic-primarykey-docs-update

Added docs for compound primary key
Fixed wrong syntax when no columns are set
Merge pull request #145 from johanneslumpe/patch-2

For for incorrect sql (aggregates with columns)
docs update for 0.5.3
release 0.5.3