Merge branch 'release-0.5' into develop
Bumped version to 0.6-dev
Improved stats handling, added sorted dump
Added Model::all()
Removed require-dev from composer.json

Using phar archives for those utilities, and require-dev is installed by
default so it makes a bit of a mess.
Updated TODO
Added a simple performance test suite.
Additional badges for README.md
Minor formatting change.
Added check that PK values must be scalars.
Made filters work when equating with null

filter('column', '=', null) will now render as "column IS NULL", and
filter('column', '!=', null) will render as "column IS NOT NULL".
BC BREAK: Moved filters to Filter namespace
Fixed tests for new Filter namespace

Also split FilterTest into multiple classes.
Implemented raw filters
Additional warning for raw filters in docs
Removed logging
Moved connection creation to a separate method
Implemented query events
Forgotten include in the performance test
Fixed incompatibility in tests for PHP 5.3