Make client api like participant. Add one-time callback option for InternalParticiant. Minor cleanup. refs #13 refs #28 refs #9
Cap number of sequence IDs per source remembered in Peer. refs #29
Implement comments from nialscorva, and add es5 shim file. refs #9 refs #11 refs #13 refs #28

Minor code cleanup, and provide implementation of all standard es5 capabilities in es5-shim.min.js. Remove polyfill fm peer.js in lieu of this.
For InternalParticipant#cancelCallback, return true if the callback was present, false otherwise. refs #9 refs #11 refs #13 refs #28