Common: redefined math functions as templates
Common: corrections to String class

* Fixed ReadCount() setting wrong string length if stream data contained null-terminators;
* Removed excessive strlen() calls in Compare* methods;
* Made equality operators const;
* Removed subscript operator bounds check;
* Renamed String::Release() method to String::Free() and made it public to allow user force string buffer deallocation when needed;
* Inlined few intensively used methods.
Common: changed the rules of how String::FindSection works

String::FindSection now takes field indexes as parameters, instead of separator indexes.