clean up members, arguments, and formatting

[incanus]

Hit some weirdness over in #928 with the naming here and posting some cleanups.

• Since we're dealing with both VectorTileData (base: TileData) and VectorTile classes, we should refer to raw data retrieved from a vector tile download and used to instantiate a VectorTile as raw_data, not just data.
• The VectorTile instantiated is now called vector_tile, not vector_data.
• The VectorTileData& tile is not ideal, since elsewhere in the project we also have a Tile class, but for the purposes of convenience throughout the implementation, it stays.
• Overall formatting changes like ClassName& argument_name — reference & next to type, then a space, then the variable name with _ and not camelCase.

[incanus]

BTW explicit mention of vector tiles will go away soon, once #928 lands and I'm back on #893 ;-)

[jfirebaugh]

Looks good but we are moving toward camelCase variable names, not underscore: #399.

[incanus]

Cool, will fix while I'm in there.

[incanus]

Moved to camelCase for members and externally-available arguments.