title: Is it possible to extend the types that are supported by the Phoenix generator?
body: <p>Is it possible to extend the set of types for a generator? For example if have a custom Ecto type <code>:money_with_currency</code> and I want to use that type when generating a new context. This type is not a type that Phoenix supports by default. In a lot of projects I find myself creating a new type and would like to leverage the power of phoenix generators.</p>
  <h2>Desired outcome</h2>
  <pre class="lang-bash prettyprint-override"><code>mix phx.gen.context Invoicing Package packages price:money_with_currency
  
  # success
  </code></pre>
  <h2>Actual outcome</h2>
  <pre class="lang-bash prettyprint-override"><code>mix phx.gen.context Invoicing Package packages price:money_with_currency
  
  ** (Mix) Unknown type `:money_with_currency` given to generator. The supported types are: array, binary, boolean, date, decimal, enum, float, integer, map, naive_datetime, naive_datetime_usec, references, string, text, time, time_usec, utc_datetime, utc_datetime_usec, uuid
  </code></pre>