Implemented struct parser

src/errors/Common.go

@@ -6,6 +6,7 @@ var (
 	ExpectedFunctionParameters = &Base{"Expected function parameters"}
 	ExpectedFunctionDefinition = &Base{"Expected function definition"}
 	ExpectedIfBeforeElse       = &Base{"Expected an 'if' block before 'else'"}
+	ExpectedStructName         = &Base{"Expected struct name"}
 	InvalidNumber              = &Base{"Invalid number"}
 	InvalidExpression          = &Base{"Invalid expression"}
 	InvalidRune                = &Base{"Invalid rune"}