fix builtins implemented in C++ to return UTF-8 Strings

added rb_utf8_str_new() helpers for creating UTF-8 Strings
fixed compiler warnings

- warning: deprecated conversion from string constant to ‘char*’
- warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument has type ...::size_type
Merge pull request #34 from lslezak/utf8_builtins

fix builtins implemented in C++ to return UTF-8 Strings
Merge pull request #35 from lslezak/fix_warnings

fixed compiler warnings
ensure that ruby bindings run only ruby clients
cache loaded namespaces to be more efficient and prevent memory leaks
more memory leak fixes
decrease log verbosity
allow division by zero as ycp also allows it