Created CanBuildFrom from ValueSource[_] -> RasterSource

This is for mapping a ValueSource to a raster, for instance if you
rasterize a polygon, you should get a RasterSource back.

Changed the .info on RasterSourceLike to check if the definition is
for a catalogued raster; if so, pull the info from the catalog, else
build an info off of the raster definition.
Fixed typos in README.md
Merge pull request #700 from BrandonNoad/fixTypos

Fixed typos in README.md
Merge remote-tracking branch 'upstream/master' into ValueSource/RasterSource
Merge pull request #701 from lossyrob/ValueSource/RasterSource

Created CanBuildFrom from ValueSource[_] => RasterSource