Modification to implementation of round() such that it returns a float and accepts a places argument (fixes #3473).

This also involved moving some functions around to get the hierarchy correct and the documentation for frexp was modified such that it was clear that it can return a float in either the range [-1, -0.5] or [0.5, 1].

web/news.txt

@@ -45,6 +45,11 @@ Changes affecting backwards compatibility
 - The path handling changed. The project directory is not added to the
   search path automatically anymore. Add this line to your project's
   config to get back the old behaviour: ``--path:"$projectdir"``.
+- The ``round`` function in ``math.nim`` now returns a float and has been
+  corrected such that the C implementation always rounds up from .5 rather
+  than changing the operation for even and odd numbers.
+- The ``round`` function now accepts a ``places`` argument to round to a
+  given number of places (e.g. round 4.35 to 4.4 if ``places`` is 1).
 
 
 Library Additions