bez_smooth: bezier smooth
In dblodgett-cycling/gpxR: GPX R Tools for Fake Cycling

replaces the track points between start and end points with a bezier curve.

1	bez_smooth(track, start_id, end_id, control, n_points = 10, reset_ids = FALSE)

`track`	sf data.frame gpx track
`start_id`	integer start track_seg_point_id
`end_id`	integer end track_seg_point_id
`control`	numeric of length 2 or equivalent that can be coerced to matrix. must be in same projection as track.
`n_points`	integer number of points to create along the new curve.
`reset_ids`	logical if FALSE, track ids will not be reset and new points will not have ids.