glossary: Make objects explicitly unordered and forbid duplicate names

Pin down our JSON definition to a particular RFC (which we can
explicitly bump if neccessary), instead of referencing the floating
JSON homepage.

Explicitly make objects unordered and forbid duplicate names to avoid
relying on unportable behavior.  RFC 7159 is a bit more relaxed [1]:

  The names within an object SHOULD be unique.

but warns [1]:

  An object whose names are all unique is interoperable in the sense
  that all software implementations receiving that object will agree
  on the name-value mappings.  When the names within an object are not
  unique, the behavior of software that receives such an object is
  unpredictable.  Many implementations report the last name/value pair
  only.  Other implementations report an error or fail to parse the
  object, and some implementations report all of the name/value pairs,
  including duplicates.

The RFC also warns about order portability [1]:

  JSON parsing libraries have been observed to differ as to whether or
  not they make the ordering of object members visible to calling
  software.  Implementations whose behavior does not depend on member
  ordering will be interoperable in the sense that they will not be
  affected by these differences.

And has some (informative?) language about entries being unordered
[2]:

  An object is an unordered collection of zero or more name/value
  pairs...

[1]: https://tools.ietf.org/html/rfc7159#section-4
[2]: https://tools.ietf.org/html/rfc7159#section-1

Signed-off-by: W. Trevor King <wking@tremily.us>

glossary.md

@@ -20,6 +20,8 @@ On Linux, a leaf in the [namespace][namespaces.7] hierarchy in which the [config
 ## JSON
 
 All configuration [JSON][] MUST be encoded in [UTF-8][].
+JSON objects MUST NOT include duplicate names.
+The order of entries in JSON objects is not significant.
 
 ## Runtime
 
@@ -31,6 +33,6 @@ It reads the [configuration files](#configuration) from a [bundle](#bundle), use
 On Linux, a leaf in the [namespace][namespaces.7] hierarchy from which the [runtime](#runtime) process is executed.
 New container namespaces will be created as children of the runtime namespaces.
 
-[JSON]: http://json.org/
+[JSON]: https://tools.ietf.org/html/rfc7159
 [UTF-8]: http://www.unicode.org/versions/Unicode8.0.0/ch03.pdf
 [namespaces.7]: http://man7.org/linux/man-pages/man7/namespaces.7.html