Docstring fixes in sympy.tensor.tensor

Added new example about symbolic data inside a tensor.
diffgeom docstring fixes
wrapped lines longer than 80 chars
Improved Documentation and added _eval_conjugate method to gammma
Added cross-references and references
Added _eval_conjugate to loggamma
eval_conjugate for lowergamma, uppergamma
Clean up documentation for Gamma functions
Fix evaluation of conjugates of incomplete gamma functions
Implement more special values for the polygamma function
Improve doc for gamma functions
Remove some functionality that breaks hyperexpand
See also fix
Merge pull request #2797 from Upabjojr/docstring_diffgeom_fix

diffgeom docstring fixes
Merge pull request #2800 from raoulb/newer_gamma

Newer gamma
Merge pull request #2796 from Upabjojr/tensor_document_symbolic_values

Docstring fixes in sympy.tensor.tensor
Finalised docs:1, rectified doctests
Merge branch 'master' of https://github.com/sympy/sympy into vectormove