Improved fast hypergeometric function

hypergeomq improved and simplified. Some parts moved into general utility functions. Fixed one bug that may have been due to update in MuPAD -this might break the function for older version of Matlab, but I can't test (tried in R2012b and it was fine).

New private utility functions: float2str and sym2float for use by fast symbolic math functions. These are smart and more accurate than what hypergeomq used -but slower in some cases, e.g., values with very large or very small exponents.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>