Updated voxel_slices

Various updates to voxel_slices to improve functionality, particular with respect to adding overlay images.

Proper initial release

Conversion of ANTs warps to float32 was causing weird issues. This version removes it as an option.

ants_tbss is now working properly again.

Initial release

This is the initial release (v 0.0.2) for ants_tbss.
voxel_slices is also included as useful tool for check registrations and brain extraction.

The sdist was created with python 3.7.