- Use new features of OpenSCAD-2019.05 to refactor internal implementation.
- Delete the `log` module which is never used.
- Directory changed.
- `m_cumulate`, `m_mirror`, `m_rotation`, `m_scaling`, `m_shearing` and
`m_translation` are moved into the `matrix` directory.
- `turtle2d` and `turtle3d` are moved into the `turtle` directory.
- `parse_number`, `split_str` and `sub_str` are moved into the `util`
- New modules and functions.