Add method to init db with schema

This is better than maually running `sqlite3 /tmp/flaskr.db < schema.sql`
Add link to original Flask tutorial code
Add code to request db connections
Add code to fetch entries from db
Add code to write accept new entries, save to db and redirect to
show_entries.
Add code for login and logout

The logout message uses the pop() method where it pop's "logged in"
value from session dictionary. Avoids having to check if the user was logged in
to perform log out. Finally, the user is redirected to show_entries
Add templates for layout, show_entries and login

The templates are using Jinja2 syntax. show_entries.html
is extended by layout.html (a case of template inheritance) thus
reusing layout of the website in all pages.
Add style

This makes the blog application look visually appealing. I copy
pasted this stuff.
Update README.md