Several new Core features:

- new TPRegexp class by Eddy Offermann using the PCRE library for powerful
  regexp matching. TPRegexp is fully integrated in TString and can be
  used like TRegExp. For more see the TPRegexp clas description.
- Extended TString::Atoi(), Atof(), IsDigit() and new IsFloat() by
  John Frankland. For more see the method description.


git-svn-id: http://root.cern.ch/svn/root/trunk@13456 27541ba8-7e3a-0410-8455-c3a389f83636