Get $env easier with $self->env

[MaxPerl]

Hello Martin,

I test at the moment the dev branch with a very basic PSGI Application. And I thought it could be a good idea to get $env easier through $self->env. I know one can get it through $self->query->env, but I think becaus of the importance of the $env hash in PSGI Application, an own method is justified...

I propose that the $env can be pass in the new method new('ENV' => $env) and in the run_as_psgi($env) method. The first should no backward compatibility problem. The second can lead to some conflicts with plugins and modules (at least the comment in the run_as_psgi function says that some plugins need special arguments..)