Vector Tile Support

[rgreenwood]

MapServer has had a "MVT" output format since at least version 7.4 (maybe 7.2?) which creates vector tiles. MapCache has similarly supported MT format since version (?). The only documentation is RFC 119. Some mention of this functionality in the regular documentation would put MapServer on the MVT server map (sorry for the bad pun).

[jmckenna]

thanks @rgreenwood (and the pun is appreciated, ha)