String::upper() no longer modifies the String itself
Added a test for String::upper()
Merge pull request #305 from TsudaKageyu/fix-string-upper

String::upper() no longer modifies the String itself
Fixed a wrong default parameter of String::ctor()
Amended some comments about the Type parameters of String::ctor()
Merge pull request #311 from TsudaKageyu/string-default-param

Fixed a wrong default parameter of String::ctor()