[Cython] Added physical constants to Sphinx docs

doc/sphinx/cython/constants.rst

@@ -0,0 +1,54 @@
+.. py:currentmodule:: cantera
+
+Physical Constants
+==================
+
+These values are the same as those in the Cantera C++ header file ct_defs.h.
+
+.. data:: Avogadro
+
+   Avogadro's Number, /kmol
+
+.. data:: GasConstant
+
+   The ideal gas constant in J/kmol-K
+
+.. data:: OneAtm
+
+   One atmosphere in Pascals
+
+.. data:: Boltzmann
+
+   Boltzmann constant
+
+.. data:: Planck
+
+   Planck constant (J/s)
+
+.. data:: StefanBoltz
+
+   The Stefan-Boltzmann constant, W/m^2K^4
+
+.. data:: ElectronCharge
+
+   The charge on an electron (C)
+
+.. data:: ElectronMass
+
+   The mass of an electron (kg)
+
+.. data:: Faraday
+
+   Faraday constant, C/kmol
+
+.. data:: lightSpeed
+
+   Speed of Light (m/s).
+
+.. data:: permeability_0
+
+   Permeability of free space :math:`\mu_0` in N/A^2.
+
+.. data:: epsilon_0
+
+   Permittivity of free space (Farads/m = C^2/N/m^2)

doc/sphinx/cython/index.rst

@@ -11,3 +11,4 @@ Contents:
    transport
    zerodim
    onedim
+   constants