Rid-kit

fix customized CV bugs

Fix customized CV file bugs.

Main features
- Refactor the Rid-kit by [dflow](https://github.com/deepmodeling/dflow) #8
- Support Gromacs and Lammps as MD engine 8
- Add DP potential support 8
- Add constrained MD estimator as new mean force estimator 13
- Refine documents, examples and README files.

Here we provide an easy-installer script for the installation of software dependence. One may want to install all the software need in RiD through the command `sh rid-env.sh`. This package is only for the environment of RiD-kit.
**Please note that this package will install TensorFlow 1 with C++ interface, Gromacs 2019.2 and modified PLUMED2, by Conda, which means `rid-kit` itself and `dpdispatcher` will not be installed in this script so that you should follow the instructions to install them in Tutorial.**