Add analyzer for metadynamics, including sum hill, reweighting, drawing free energy profile and find MEP with String method.
These changes are inspired by [Metadynminer](https://github.com/spiwokv/metadynminer) as well as its Python version [Metadynminer.py](https://github.com/Jan8be/metadynminer.py) and [stringmethod](https://github.com/apallath/stringmethod). And the implementation refered to these projects.
Thanks!
And for detail of these methods, please refer to the following papers.
> - G.A. Tribello, M. Bonomi, D. Branduardi, C. Camilloni, G. Bussi. "PLUMED2: New feathers for an old bird." Comput. Phys. Commun. 185, 604 (2014), http://dx.doi.org/10.1016/j.cpc.2013.09.018
> - Tiwary, P.; Parrinello, M. A Time-Independent Free Energy Estimator for Metadynamics. J. Phys. Chem. B, 119(3), 736–742 (2015), https://doi.org/10.1021/jp504920s
> - Weinan E, et al. "Simplified and improved string method for computing the minimum energy paths in barrier-crossing events", J. Chem. Phys. 126, 164103 (2007), https://doi.org/10.1063/1.2720838
**Full Changelog**: https://github.com/Cloudac7/miko-analyzer/compare/v0.3.2...v0.3.3