ARI - implement allowMultiple for parameters

Swagger allows parameters to be specified as 'allowMultiple', meaning
that the parameter may be specified as a comma separated list of
values.

I had written some of the API docs using that, but promptly forgot
about implementing it. This patch finally fills in that gap.

The codegen template was updated to represent 'allowMultiple' fields
as array/size fields in the _args structs. It also parses the comma
separated list using ast_app_separate_args(), so quoted strings in the
argument will be handled properly.

Review: https://reviewboard.asterisk.org/r/2698/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396122 65c4cc65-6c06-0410-ace0-fbb531ad65f3