Legendre polynomial documentation

[M Joonas Pihlaja]

Hi,

The reference manual's entries for the array versions of the 
associated Legendre polynomials and spherical harmonics are a 
little confusing I think.

1) The _array function documentation uses the absolute value |m| 
as the lower bound of the array indices yet also specifies m
>= 0.  Why the absolute value if negative m aren't allowed after
all?

2) The docs say the _deriv_array functions compute "optionally 
their derivatives", which made me think that the 
result_deriv_array parameter could be passed in as NULL if one 
didn't need the derivatives.  Turns out that's not what it meant. 
:)  The phrasing could be a little bit more explicit IMHO.

Cheers,

Joonas