Modifications to mdlformat.h.
Modifications to mdlformat.h.

* Use a types that are match other code (e.g. unsigned char for
  atomic number).
* Improve documentation.
* Some style clean up. I left the one-line case/if/return/break
  statements in some places, invoking the OpenChemistry coding
  style's infamous General Exception.
* Add an atomValence method that indicates overbonded atoms.

Change-Id: I28a8d721f06a24bc92dc04251a18b22188599eb1

OpenChemistry/avogadrolibs,wadejong/avogadrolibs,cjh1/mongochemweb-avogadrolibs,cjh1/mongochemweb-avogadrolibs,wadejong/avogadrolibs,cjh1/mongochemweb-avogadrolibs,OpenChemistry/avogadrolibs,ghutchis/avogadrolibs,ghutchis/avogadrolibs,ghutchis/avogadrolibs,ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,OpenChemistry/avogadrolibs,ghutchis/avogadrolibs,cjh1/mongochemweb-avogadrolibs,wadejong/avogadrolibs,OpenChemistry/avogadrolibs,wadejong/avogadrolibs