Additional Functional and Efficiency for Non-consistent Functionals

This extension has been utilized for benchmarking recently. It seems haven't experienced errors or faulty results, and I'm quite satisfied with efficiency (given enough memory though).
I think algorithms of RI-JK reference RI-PT2 doubly hybrid polarizability and gradient could freeze here. Space of efficiency improvement is probably limited.

New functionals:

• DSD family with D3(BJ) dispersion correction (version 2013): DSD-PBEP86-D3, DSD-PBEPBE-D3, DSD-BLYP-D3, DSD-PBEB95-D3
• B2PLYP-D3
• Non-consistent functionals: HF-B3LYP, HF-PBE0 (no PT2 contribution, which was previously supported for calculation, but not defined as a keyword)

Other features:

• Non-consistent functionals energy, gradient, polarizability calculation now won't call any PT2 modules, and auxiliary basis integrals for PT2 will not be generated.
• Change default dft integral engine to LibXC. For most cases of mine, LibXC performs more efficient, and LibXC supports more functionals; but subtle errors are more likely to happen. BLYP and PBE based functionals seems no problems, so most GGA based doubly functionals is probably okay.
• Gradient contribution from GGA functional now directly calls PySCF's utilities, which is faster than my previous implementation.

Possible bugs:

• P86 correlation functional energy value have very subtle difference compared to other softwares.

Algorithm Change

Change default gradient_gga engine to PySCF's hessian.rks._get_vxc_deriv1 and grad.rks.get_vxc

Minor add functionality

Added more functionals since last update:

• revXYG3, XYG5, XYG6, XYG7, revXYGJ-OS, XYGJ-OS5
• B2GPPLYP, LS1DH-PBE

Added setup.py and updated README.md

Initial release

Ability:

• Restricted and unrestricted available
• Single point energy, gradient, polarizability
• Currently only RI-JK density-fitting is fully supported
• Supported functionals:
  • MP2
  • XYG3
  • XYGJ-OS (not in LT-SOS form)
  • xDH-PBE0 (not in LT-SOS form)
  • B2PLYP
  • mPW2PLYP
  • PBE0-DH
  • PBE-QIDH
  • PBE0-2
  • Other functionals is still possible to be defined manually by xc argument, if functional is XYG3-like or B2PLYP-like, and the gga parts could be evaluated by libxc (energy, gradient) and xcfun (polarizability)