* added ui for derivative impl
* Add derivative computation for bezier-rs library
* integrate devivative ui with library
* Add implementation for the normal function
* Update rustdoc comments
* Rename handles and getters, add tangent function
* Rename variables, address nits
Co-authored-by: Rob Nadal <robnadal44@gmail.com>
Co-authored-by: Thomas Cheng <contact.chengthomas@gmail.com>
Co-authored-by: ll2zheng <Linda Zheng>