This returns URLs with Markdown enabled. Part of #14

Leave out -u option in writeas auth command

Instead of writeas auth -u <username>, now you can just use
writeas auth <username>

Only with `writeas publish` right now, and only if posts directory has
already been set up.

Adds new `writeas publish <file>` command

This configures a directory for posts and downloads all posts on the
authenticated account into the directory, organizing collection posts
into their own subdirectories.

This adds a new parameter that determines whether or not authentication
is required, and also returns an error now.

Closes #16

If you're logged in, now requests will be made with the saved token

Instead of using an INI file for the access token, this stores it and
other user information in a single JSON file.

Adds new `writeas auth` command and saves user's access token to a new
local configuration file.

This closes #10 / T191

This closes #9