Per chat, add an optional maxsize param s.t. bridge will check the buffer size of generated vector tiles and error out if tiles exceed a certain size.

• Bridge already parses and respects the query string as a way of passing options in a URI -- e.g. bridge:///path/to/some/xml?maxsize=1000000 would get parsed right now onto the source object, but nothing is done with it (https://github.com/mapbox/tilelive-bridge/blob/master/index.js#L23-L32)
• You'll want to enforce this at the last stage here https://github.com/mapbox/tilelive-bridge/blob/master/index.js#L195
• And of course, test : )