v0.5.0 - reactive docking

What's new

• Support for reactive docking (chemrxiv, instructions)
• Easier to define new atom types from SMARTS #56
• Minimal support for receptor preparation (instructions)
• Modified API

Fixes and other improvements

• refuses to write PDBQT with Nan and Inf charges by default #55
• wildcards accepted by mk_export.py, e.g. mk_export.py *.dlg #43
• option -c in mk_export.py writes SDF with top pose from each cluster from autodock-gpu #38
• set grid box size and center based on existing ligand efb14bc
• handle H isotopes #39
• mk_export.py reads gzipped files
• fix bond typing in PDBQTMolecule for single atom molecules #57
• other minor fixes and improvements