fast3tree v0.4.1

Update the docstring for fast3tree.query_nearest_distance. When one of the points in the tree is located exactly at center, this function would return the distance to the next nearest point. This behavior is not directly obvious and the new docstring states this feature clearly.

Thanks to @chto for noticing this.

fast3tree v0.4.0

• Several under-the-hood updates were made.
• License updated to GPLv3.
• First release after this project moved from bitbucket to GitHub.