Update Parsoid content-type to 1.2.1
Update Parsoid content-type to 1.2.1

Also:

- Include charset parameter, as in the response.
- Link to the mediawiki.org documentation page.

d00rman/restbase,milimetric/restbase,wikimedia/mediawiki-services-restbase,milimetric/restbase,cscott/restbase,gwicke/restbase,Pchelolo/restbase,gwicke/restbase,eevans/restbase,Pchelolo/restbase,eevans/restbase,wikimedia/restbase,wikimedia/mediawiki-services-restbase,wikimedia/restbase,cscott/restbase,inverno/restbase,inverno/restbase,d00rman/restbase