Added proposal 13121
Fixed bug in learnign2domain doctypes plugin
Implemented simple FO output using instream-foreign-object to hold the MathML markup
Removed obsolete file, added language for ux-windowref to 13060
Added ditaarch namespace declaration to all .rng files
correctec RNG proposal for ditaarch:longName, externalref attributes
Set up idElements pattern and used from basetopic.mod
Integrated use of idElements pattern in the base modules and in the proposal
Final editorial pass over proposal. Integrated changes for 13121