Standardize and create rules for the names of chemical species in CCPPStandardNames

[mkavulich]

Following a productive discussion today related to PR #44, we have agreed that we need a path forward for standardizing and disambiguating the standard names for chemical species. The proposed changes (open for discussion of course) are as follows:

1. Currently the StandardNamesRules.rst document specifies a list of acceptable "Chemical Species". This list will be deprecated/removed, and in its place a new rule will be added: Any chemical species used in a standard name (e.g. the "ch4" in volume_mixing_ratio_of_ch4) should have its own standard name entry, with an unambiguous description of the chemical species (this will become especially important as more complex species are introduced to the standard names repository, with isomers and other complications).
2. When possible, the standard name for the species should be the chemical formula specified by the Hill System, but in cases of ambiguity due to isomers or other factors (e.g. CFC-113) an unambiguous common name may be decided on at the time of addition.
3. Existing spelled-out chemical species names will be converted to use the new formula-based standard name (e.g. index_of_ozone_mixing_ratio_wrt_moist_air_in_tracer_concentration_array --> index_of_o3_mixing_ratio_wrt_moist_air_in_tracer_concentration_array