Eta^3 Spline path planning

This is a path planning with Eta^3 spline.
Code Link
- class PathPlanning.Eta3SplineTrajectory.eta3_spline_trajectory.Eta3SplineTrajectory(segments, max_vel, v0=0.0, a0=0.0, max_accel=2.0, max_jerk=5.0)
eta3_trajectory
- input
segments: list of eta3_trajectory_segment instances defining a continuous trajectory