[with patch, positive review after a fast re-reading] convert sage.functions.* docstrings to Sphinx

[hivert]

I've found some minor problem in the patch:

-  Each *Legendre polynomial* `P_n(x)` is an $n$-th degree polynomial. 

Should be

-  Each *Legendre polynomial* `P_n(x)` is an `n`-th degree polynomial. 

And a little bit lower:

 The *Legendre function of the second kind* $Q_n(x)$ is another 

Should be

 The *Legendre function of the second kind* `Q_n(x)` is another 

A whole section

Implemented methods: 
  9 latex outout 
  10 __call__ 
[...]
  39 extend_by_zero_to 
  40 unextend 

seems to have vanished.

[hivert]

I've manually edited the patch to fixes the two "$" vs "`" problems. The corrected patch should follow.

The section implemented methods is removed on purpose (it is redundent with the code). Otherwise it seems Ok.

As for combinat, my rereading was a fast rereading. In particular, There are a lot of formulas that needs time to be checked carfully.

[hivert]

New patch with hand fix.

[mhansen]

I put these changes in the fixes.patch in #5330.

[mabshoff]

Merged sage.functions-final-fixed.patch in Sage 3.4.alpha0.

Cheers,

Michael