Changing . to % to access components of derived types

[certik]

Some related links:

• What's your experience with using % for accessing object members?
• Idea: Support dot (`.`) as an alternative to the `%` operator · Issue #199 · lfortran/lfortran · GitHub
• Idea: Support dot (`.`) as an alternative to the `%` operator (#84) · Issues · lfortran / lfortran · GitLab