Added memory check when consuming a message.

The consumer will be stopped if the available memory is not enough.

Fixed memory calcul.
Fixed composer dependencies

Rolling back to a range of version.

Use ~2.0 for yaml component.

Use ~2.0 for console component.
Removed unnecessary configurations in travis.
Update README.md
Merge pull request #99 from blaugueux/patch-composer

Fixed composer dependencies
Merge pull request #98 from blaugueux/memory-limit

Added memory check when consuming a message.
Merge pull request #101 from quantizer/patch-1

Update README.md