Symbolic-regression-toolkit

- Updated documentation
- Added the change log

**New Features:**

- Added Dataset and benchmark objects that create evaluators for Symbolic Regression models
- Added modified versions of feynman and nguyen benchmarks

**Bug Fixes:**

- Fixed expressions with constants only evaluating to one value instead of an array

- Project restructure

**New Features:**

- Added documentation
- Expanded upon examples

- Initial release
- Expression compilation
- Parameter estimation
- Model evaluation
- Examples for parameter estimation and performance evaluation