Update association docs.
closes #173
Bring back tabs

It seems github converts tabs to 4 spaces when rendering markdown.
My previous commit reduced tabs to two spaces. Anyways, tabs are back.
Adds AggregateFunctions.limit() and changes Readme to avoid confusion (#172)
Passes driver name (mysql, pg, ..) to ORM and Model constructor
Passes driver name (mysql, pg, ..) to AggregateFunctions constructor
Checks for driver debug flag and prints debug line in AggregateFunctions (#171)
Changed sqlite3 from v 2.1.5 to 2.1.7 to successfully compile
Actually 2.1.7 instead of 2.1.x
Added Hook 'beforeValidation' prior to _all_ validations

`beforeValidation` will now be called before the `required` check and before `beforeCreate` and `beforeSave`.  Also the Readme.md file was updated to reflect this addition.
Added Hook 'beforeValidation' prior to _all_ validations

`beforeValidation` will now be called before the `required` check and before `beforeCreate` and `beforeSave`.  Also the Readme.md file was updated to reflect this addition.
Fixed a bug when calling save() on an Instance

Previously, if you called save() on an Instance without passing a callback argument **and** made no changes to the extra variables in that Instance, in the saveInstanceExtra function it assumed the presence of a callback and would throw an error.
Merge pull request #177 from leechfarm/master

Added Hook 'beforeValidation' and updated docs
Adds test for beforeValidation hook
sql-query@0.0.23

Fixes postgres Date escaping
Updates Readme driver dependency versions
Avoids JSON parsing values when they are already objects (and not string buffers) (#168)
Adds Hooks.wait to later on use it for async hooks (#167)

For now, the only hook that accepts async is beforeRemove. This is an
implementation test and will propagate to others if it fits.
Changes beforeCreate, beforeSave and beforeValidation to use Hooks.wait() (#167)
Updates Readme to explain async before* hooks (#167)
Added support for non-autoincrement key fields; check db driver info exists before applying it to data