Re #9777. Adding attributes tags to fit functions.

Code/Mantid/docs/source/fitfunctions/Abragam.rst

Code/Mantid/docs/source/fitfunctions/BSpline.rst

...Mantid/docs/source/fitfunctions/BackToBackExponential.rst

Code/Mantid/docs/source/fitfunctions/BivariateNormal.rst

Code/Mantid/docs/source/fitfunctions/Chebyshev.rst

Code/Mantid/docs/source/fitfunctions/ChudleyElliot.rst

Code/Mantid/docs/source/fitfunctions/CompositeFunction.rst

Code/Mantid/docs/source/fitfunctions/Convolution.rst

Code/Mantid/docs/source/fitfunctions/CubicSpline.rst

Code/Mantid/docs/source/fitfunctions/DSFinterp1DFit.rst

...Mantid/docs/source/fitfunctions/DiffRotDiscreteCircle.rst

Code/Mantid/docs/source/fitfunctions/DiffSphere.rst

Code/Mantid/docs/source/fitfunctions/ExpDecay.rst

Code/Mantid/docs/source/fitfunctions/ExpDecayMuon.rst

Code/Mantid/docs/source/fitfunctions/ExpDecayOsc.rst

Code/Mantid/docs/source/fitfunctions/FickDiffusion.rst

Code/Mantid/docs/source/fitfunctions/FlatBackground.rst

Code/Mantid/docs/source/fitfunctions/GausDecay.rst

Code/Mantid/docs/source/fitfunctions/GausOsc.rst

Code/Mantid/docs/source/fitfunctions/Gaussian.rst