Correct resolution for rotated rasters
Merge pull request #61 from AsgerPetersen/rasterresolution

Correct resolution for rotated rasters
Merge branch 'master' of https://github.com/brendan-ward/rasterio into brendan-ward-master
Modifications to pull request #62.

I made rasterize_features redundant. With a single list comprehension
a list of features can be turned into a list of (geom, value) pairs.

I made the default value 255 to match other rasterio functions.

_rasterize() now takes responsibility for converting Python geoms to
JSON and can now burn shapes into an existing image array.
Sometimes None is the real value of CRS.
Next version will be 0.8
Change sense of mask for shapes().
Test for nonzero length of proj string.

Before exporting to PROJ.4.
Encode JSON using UTF-8.
Remove const declaration.
Fixed example and improper pattern for setting options passed to GDAL in rasterize function.