fixed flash parameter type

url parameter is not only string according to the api docs:
http://api.cakephp.org/class/controller#method-Controllerflash
Merge pull request #490 from ravage84/patch-2

fixed flash parameter type
Fix code example.
Added self HABTM documentation
Fix code example
Merge pull request #491 from WyriHaximus/master

Added self HABTM documentation
Fixed wrong parameters of Cache::write
Merge pull request #492 from CanesCZ/patch-1

Fixed wrong parameter of Cache::write
Adding docs for multiple counterCache