Support specifying column name in MapConfig

Closes #191
Includes testcase
Requires development version of grainstore
Add support for raster layers (#191)

Requires unofficial grainstore version.
Includes small testcase.
Accept MapConfig version 1.2.0, properly use 1.2.0 for raster use

Also reduce tolerance of equality test for rasters
Update viewer to accept a MapConfig
Strip newlines from MapConfig string, so it's easier to type
Add suppor for png32 and png8 tile formats

Also improves a testcase to cleanup after itself (see #149)
Really pass png format on to tilelive-mapnik

See https://github.com/mapnik/mapnik/issues/2303#issuecomment-49061886
Pretty-print JSON of MapConfig
Upgrade grainstore
Merge branch 'master' into pgraster

Conflicts:
	NEWS
	package.json
	test/acceptance/multilayer.js
Do not pass "png.+" formats to mapnik
Fix test after dropping support for user-requested "png32" format
Revert unneeded changes in TileliveAdaptor code
Modifies strk/pgraster to support gcols to use objects for configuring type/name for the geom/raster column
Merge branch 'master' into pgraster
Merge branch 'master' into pgraster

Conflicts:
	NEWS
	package.json
Upgrades grainstore dependency to be able to use 2.3.0 carto styles
Merge branch 'master' into pgraster

Conflicts:
	package.json
	test/acceptance/server_gettile.js
Merge branch 'master' into pgraster
Merge branch 'master' into pgraster

Conflicts:
	package.json