Update ofUtils_functions.markdown

Okay, now I only changed the description and left the function signatures untouched. (Looking at the source files ofUtils.h and ofUtils.cpp the first signature of ofSplitString in this description file seems wrong though, since delimiter doesn't have a default value in the current version of oF.
Merge pull request #309 from chphmh/patch-2

Update ofUtils_functions.markdown (replaces #308)