Add markdown support for summary (#482)

* Add markdown support for summary

* Save both md and html summary

migrations/postgres/2019-03-16-143637_summary-md/down.sql

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+-- This file should undo anything in `up.sql`
+ALTER TABLE users DROP COLUMN summary_html;

migrations/postgres/2019-03-16-143637_summary-md/up.sql

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+-- Your SQL goes here
+ALTER TABLE users ADD COLUMN summary_html TEXT NOT NULL DEFAULT '';
+UPDATE users SET summary_html = summary;