#22 - Implement method CppStringT::isalpha()

Completed.
Added namespace `pcs`.
Modified forward declarations.
Added chars classification templated functions and their specializations for alpha chars.

Author: schmouk

cpp-strings/cppstrings.cpp

@@ -20,6 +20,7 @@
 */
 
 #include "cppstrings.h"
+using namespace pcs;
 
 /**
 * Notice: this module is for tests and validation purposes only.