www/remark42: update to 1.18.0

While here, bring the rc script in line with upstream's options:

• Rename remark_disable_fancy_html_formatting to remark_disable_fancy_text_formatting; the old name exported a variable the server does not read.
• Rename the remark_auth_enable and remark_auth_email_subject defaults to remark_auth_email_enable and remark_auth_email_subj, the names that are actually exported.
• Add remark_trusted_proxy, remark_auth_ttl_jwt, remark_auth_ttl_cookie, remark_auth_send_jwt_header, remark_auth_microsoft_tenant, remark_auth_custom_*, remark_telegram_api_url and remark_smtp_helo_host.
• Default remark_avatar_uri and remark_ssl_acme_location to the data directory instead of a path relative to the working directory.