scipy.special.legendre docstring

1. Some arguments are boolean, so use True and False instead of 0 and 1.
2. PEP8 fixes
3. Expand docstring for legendre polynomials.  Similar docstrings could be made for all the others.  I think n is an int, but [not 100% sure](http://en.wikipedia.org/wiki/Legendre_polynomials#Legendre_functions_of_fractional_order), but I don't see how http://www.wolframalpha.com/input/?i=LegendreP[2.5%2C+x] is related to `legendre(2.5) = poly1d([ 1.9207,  0.    , -1.1524, -0.    ])` so it should probably say "int" and reject non-ints?

Example is from the list at http://en.wikipedia.org/wiki/Legendre_polynomials#Recursive_definition