XEP-0390: Initiate Last Call

[horazont]

Council just voted on issuing a Last Call for XEP-0390. Please do so:

FTR, the steps are (IIRC):

• Change to Proposed
• Set an expiration date in <lastcall/>
• Send an email

[horazont]

FWIW, announcement email can be generated by send-updates.py if you have a sufficiently diffed pair of xeplist.xml

[iNPUTmice]

I've started the Last Call.