Updates Composer require from 2.0.* to 2.1.*

This reflects the current version of Sentry that should be used for projects.
Merge pull request #353 from nfeiglin/patch-1

Updates Composer require from 2.0.* to 2.1.*
Added Kohana install doc
Added model aliassing to Kohana guide
last Kohana guide tweak
Kohana guide: forgot mentioning import DB
Merge pull request #363 from happyDemon/master

Docs: Kohana install guide
Refactored ConnectionResolver to load the right database connection
class instead of only setting the right grammar. Using FuelPHP with
Postgres showed that processInsertGetId was called using the default
Processor instead of PostgresProcessor which passes an incorrect 
$sequence for Pdo::lastInsertId.
Fixed cookie handling in Laravel 4.0.*

See issue #325 for more info
Added test for jar strategy
Merge pull request #371 from levacic/feature/2.1-cookie-fix

Fixed cookie handling in Laravel 4.0.*
Update create.md

Fix missing semicolon
Merge pull request #377 from ssx/patch-1

Update create.md
Merge pull request #368 from CodeYellowBV/master

Refactored ConnectionResolver to load the right database connection
fix fuelphp docs install vendor path

Signed-off-by: Bruno Gaspar <brunofgaspar1@gmail.com>
makes user_id field nullable

If a user attempts to sign in with an account that does not exists, the exception below is thrown, because Sentry attempts to update the throttle table with a null user_id. This makes the user_id field nullable.

```
Illuminate \ Database \ QueryException
SQLSTATE[HY000]: General error: 1364 Field 'user_id' doesn't have a default value (SQL: insert into `throttle` (`type`, `updated_at`, `created_at`) values (global, 2014-03-27 08:55:12, 2014-03-27 08:55:12))
```
Updated documentation links
Update Group.php
Let ServiceProvider set the configured user model
Make userModel configurable for the ServiceProvider