Improve examples and apply consistent formatting:
* Replace wrong recipient in example by 'alice@example.org'
* Use recipient 'bob@example.com' in examples consistently
* Apply consistent formatting for revision history
Update to XEP-0420 version 0.4.0 and XEP-0434 version 0.5.0:
* Replace SCE's old 'content' element by its new 'envelope' element
* Replace SCE's old 'payload' element by its new 'content' element
* Update SCE's namespace to 'urn:xmpp:sce:1'
* Update TM's namespace to 'urn:xmpp:tm:0'
* Update namespace to 'urn:xmpp:atm:1'
Add usage of Trust Message URIs, use more precise sentences, apply consistent formatting:
* Add usage of Trust Message URIs for initial authentications
* Use 'that' instead of 'which' for restrictive clauses
* Apply consistent formatting for paragraphs and revision history
