Replaced \Symfony\Component\HttpKernel\Log\LoggerInterface with \Psr\Log\LoggerInterface.
Added psr/log to composer.json.

Symfony advises to use \Psr\Log\LoggerInterface instead of the \Symfony\Component\HttpKernel\Log\LoggerInterface. Since the symfony loggerInterface is deprecated and to be removed in 3.0.

since 2.2, to be removed in 3.0. Type-hint .
Bumped dev version to 1.3, as requested.
Merge pull request #673 from cobaltjeh/psr-logger-replacement

[Proposal] Change to the psr loggerinterface. Related issue #658