Adds an optional argument in Numeral.format for a rounding function.

The argument defaults to Math.round if undefined, so this does not
change the behaviour of Numeral for any previous use-cases.

Tests are included - all existing tests pass.
Merge branch 'master' into develop
remove whitespace
Merge branch 'pr/98' into develop

Conflicts:
	min/numeral.min.js
build