GString.opBinary

auto t1 = typeof(this)("Test ");
auto t2 = t1 ~ 'A';
assert(t2.rawString == "Test A");
auto t3 = t1 ~ cast(wchar) 'B';
assert(t3.rawString == "Test B");
auto t4 = t1 ~ cast(dchar) 'C';
assert(t4.rawString == "Test C");
auto t5 = cast(dchar) 'D' ~ t1;
assert(t5.rawString == "DTest ");