v0.3.3: Find voxel segmentation classes, apply transforms, parse m3z files

• Added support for loading affine transformation matrices, e.g., files or mri_info output that follows the FreeSurfer register.dat format.
• New group-level functions for loading stats data
• Support for parsing talairach.xfm files
• Add brainlocator class that allows to conveniently find the vertex in a surface file that is closest to some RAS coordinate.
• Add BrainVoxLocator class that allows to conveniently find the segmentation label of a voxel. Also supports finding the label of the closest voxel with non-empty (not 'Unknown') label and gives the distance to it.
• Add support for loading m3z files, like mri/transforms/talairach.m3z