Add method to atom to calculate Lewis acid/base vacancies
Add method to molecule to convert zero-order bonds to single or double bounds and adjust adjacent charges accordingly.
Add ZBO, ZCH, HYD extensions to MDL format
Stop AddHydrogens from resetting the ImplicitValencePerceived flag
Fix bug where unnecessary HYD values were written in MDL format
Remove leftover logging statements
Fix indentation
Merge remote-tracking branch 'upstream/master' into mdlextension
Improve space group support in .car files

- Support Hermann-Mauguin notation space groups with spaces and also
  the unspecified default space group.

- HM space group is enclosed within parentheses and can contain space
  between them as per the given format details in -
  http://hincklab.uthscsa.edu/html/soft_packs/msi_docs/insight980/formats980/ClassicFiles.html.

  The previous code didn't recognize such a spacegroup as it strictly
  looked for 8 fields after tokenizing them using default delimiters as
  space, tab, newline.

- It is legal to have .car files with PBC=ON and no space group defined
  in the fifth line and just have PBC and a,b,c,alpha,beta,gamma
  parameters. Such structure is considered to have lowest symmetry
  space-group as P1. This means there are no symmetry operations in play
  and all atoms are explicit within the unit cell. The .car files for
  H2O and polymers fall under this category since they are amorphous but
  are periodic.

- Added tests to ensure this is working.
Merge pull request #26 from schrodinger/master

Improve space group support in .car files
Merge pull request #18 from mcs07/mdlextension

MDL extension for zero-order bonds