Check shape and affine in masking.apply_mask
Replace astype by as_ndarray
Merge branch 'master' into roi

Conflicts:
	nisl/masking.py
Corrected a bug in regions_to_mask()
Created NiftiLabelsMasker and example

NiftiLabelsMasker computes signals from regions, plot_region_covariance_obj.py
is an example usage.