Completed implementation of unary and binary math methods from core ruby Math
module that return a single value.

All these methods are now invokable directly on NMatrix objects, e.g. m.sin

The log method takes an optional argument (the base).  Without the argument, it
defaults to natural log.  E.g.: m.log or m.log(3).

The methods hypot, atan2, and ldexp all accept NMatrix or Numeric arguments.
Where the first argument would be a scalar, you call these through the Math
module, which has been monkeypatched to know how to deal with NMatrix objects.
E.g. m.atan2(1) or Math.atan2(1, m)

All these math methods now upcast the dtype to float64 (for purposes of uniform
interface and consistency with the core math module, which also returns a float
even when the result would be an integer).  They preserve stype.