Add new script to find nearest neighbors in Freesurfer meshes.

usage: mris_nearestneighbor.py [-h] -i INPUT -p POINT POINT POINT [-k K]
                               [-r RADIUS]

Find nearest neighbors on a Freesurfer mesh.

optional arguments:
  -h, --help            show this help message and exit
  -i INPUT, --input INPUT
                        the Freesurfer mesh, f.e. -i lh.smoothwm
  -p POINT POINT POINT, --point POINT POINT POINT
                        the source point in RAS space ([mm]), f.e. -p 123.05
                        12.3 144.2
  -k K, --k K           number of points to find. DEFAULT: 1
  -r RADIUS, --radius RADIUS
                        radius [mm] to include in point search (overrides
                        -k/--k). DEFAULT: -1 to ignore.