Reads a class body
```ebnf
class_body ::= (member_flags? (T_VAR | T_STRING | T_FUNCTION))*
```
function() {
    let result = [];

    while (this.token !== this.EOF && this.token !== "}") {
      if (this.token === this.tok.T_COMMENT) {
        result.push(this.read_comment());
        continue;
      }

      if (this.token === this.tok.T_DOC_COMMENT) {
        result.push(this.read_doc_comment());
        continue;
      }

      // check T_USE trait
      if (this.token === this.tok.T_USE) {
        result = result.concat(this.read_trait_use_statement());
        continue;
      }

      // read member flags
      const flags = this.read_member_flags(false);

      // check constant
      if (this.token === this.tok.T_CONST) {
        const constants = this.read_constant_list(flags);
        if (this.expect(";")) {
          this.next();
        }
        result = result.concat(constants);
        continue;
      }

      // jump over T_VAR then land on T_VARIABLE
      if (this.token === this.tok.T_VAR) {
        this.next().expect(this.tok.T_VARIABLE);
        flags[0] = null; // public (as null)
        flags[1] = 0; // non static var
      }

      if (this.token === this.tok.T_VARIABLE) {
        // reads a variable
        const variables = this.read_variable_list(flags);
        this.expect(";");
        this.next();
        result = result.concat(variables);
      } else if (this.token === this.tok.T_FUNCTION) {
        // reads a function
        result.push(this.read_function(false, flags));
      } else {
        // raise an error
        this.error([
          this.tok.T_CONST,
          this.tok.T_VARIABLE,
          this.tok.T_FUNCTION
        ]);
        // ignore token
        this.next();
      }
    }
    this.expect("}");
    this.next();
    return result;
  }