guides/user-agent-construction.md: update jsfiddle to prerelease-0.6.0
guides/make-call.md: update jsfiddles to prerelease-0.6.0

Remove the "Displaying the Call" section, since it can now be done with
invite() arguments.
guides/receive-call.md: update jsfiddles to prerelease-0.6.0

Remove the "Register A SIP User Agent" fiddle, since it's essentially the same as the next one.
guides/reuse-mediastreams.md: update jsfiddle/code to prerelease-0.6.0
update send-dtmf guide for 0.6.0 release
Merge pull request #6 from onsip/060

060