[cache] Cache interface and in-memory implementation
[cache] README with examples
[cache] Fix typo in ArrayCache::remove()
Update references to 0.3, update lock file
Change react/promise constraints to use tilde operator
Merge remote-tracking branch 'origin/master' into 0.3

* origin/master:
  Change react/promise constraints to use tilde operator

Conflicts:
	composer.lock
	src/React/Dns/composer.json
	src/React/Stream/composer.json