Implements very simple REPL, fixes several issues found with it.

src/Parser/Lexer/Lexer.cpp

@@ -599,7 +599,7 @@ namespace MalachScript::Parser {
             case Identifier::Hash(u8"xor"):
                 return Create<LexTokenImpl<LexTokenKind::XorKeyword>>(TextSpan(start, _position));
 
-            default: return Create<IdentifierToken>(TextSpan(start, _position), Identifier(str, hash));
+            default: return Create<IdentifierToken>(TextSpan(start, _position), Identifier(str.data(), offset, hash));
         }
     }
     bool Lexer::IsAlphaNumericalOrUnderscore(char8_t c) {