Add documentation for async client#21

Merged

dbu merged 4 commits intophp-http:masterfrom

joelwurtz:feature/async

Nov 9, 2015

Commits on Nov 5, 2015

Add document for async client
joelwurtz
committed

Commits on Nov 6, 2015

Commits on Nov 8, 2015

Fix typo and rewrite tutorial part
joelwurtz
committed