Merge pull request #228 from oauth-wg/aaronpk/client-types

Clarify that there is no requirement that an AS supports public or co…

fix ref

fix references to JSON

resolves client credentials encoding issue #128

* Remove the "NOT RECOMMENDED" paragraph (but leave sentence "The parameters can only be transmitted in the request content and MUST NOT be included in the request URI.")
* Change AS requirements to MUST support post body, MAY support HTTP Basic
* Add a note about historic interop problems with HTTP Basic

closes #128

tag changelog

update changelog

update changelog

update changelog

version bump for -06

fix changelog formatting