Release version 0.3.0

Release version 0.3.0

### Added
- Cost distribution plot function.
- Heading independent near vertices procedure inspired by `nn4`.

### Changed
- Test script.
- `nn4` use Euclidean distance while independently on RRT framework cost used.

### Removed
- `opt_part` procedure (unused).

### Fixed
- Dijkstra path optimization only if goal found.
- Workaround used for optimizing part of path. There is a bug that causes
  collision when steering from `i` to `i + 1` node of path from `tlog`. See
  commit `9186f27`.