chemkin: Remove wildcard import in favor of an explict _kinetics namespace
chemkin: Remove wildcard import in favor of an explict _kinetics namespace

From PEP 8 [1]:

  Wildcard imports (from <module> import *) should be avoided, as they
  make it unclear which names are present in the namespace, confusing
  both readers and many automated tools. There is one defensible use
  case for a wildcard import, which is to republish an internal
  interface as part of a public API (for example, overwriting a pure
  Python implementation of an interface with the definitions from an
  optional accelerator module and exactly which definitions will be
  overwritten isn't known in advance).

I use a leading underscore in the name to avoid conflicts with local
'kinetics' variables, and because the imported module is a private
member of chemkin.  We don't want folks using:

  from rmgpy.chemkin import kinetics

[1]: http://legacy.python.org/dev/peps/pep-0008/#imports

KEHANG/RMG-Py,nyee/RMG-Py,faribas/RMG-Py,pierrelb/RMG-Py,nickvandewiele/RMG-Py,pierrelb/RMG-Py,comocheng/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py