Add core String test to Clownfish Perl bindings
Rename SSTR_WRAP_STR to SSTR_WRAP_UTF8
Rename a couple of variables referring to ZombieCharBufs
Fix Perl typemap for non-const Strings
Convert "const String" to "String"
Remove useless function S_grow in CharBuf
Deduplicate some CharBuf code
Fix a couple of warnings
Change String#Swap_Chars parameters to int32_t