need a function to increase the precision of a mpfr number

[michalkonecny]

I think it would be useful to have a function like:
differentPrecision :: (Rounded m1 p1) -> (Rounded m2 p2)

Rationale: It is sometimes wasteful to use the same very high precision in all sub-expressions of an expression. I would like to calculate some sub-expressions using a lower precision and then combine it with higher precision calculations. For example, when using interval Newton iterations, computing the first estimate can be usually done with a much lower precision than is required for the final result. I think it would also be beneficial to increase precision during Newton iterations.

[ekmett]

Makes sense.

With 7.10, we can drastically simplify the internals of this package as we no longer need to try to bundle a custom, patched mpfr.

Consequently, I'll probably be spending some time cleaning this package up soon, and see if we can throw this in.

[claudeha]

fixed by #27 merge

Numeric.Rounded.precRound
  :: (Precision p2, Precision p1, Rounding r) =>
     Rounded r p1 -> Rounded r p2