Support template for email subject

[snow01]

We often need template support for email subject too.

[snow01]

CI Build is failing on some test case not updated and affected by my code. See below --

1) Email templates should render html(jade) with inline CSS(less):
      Uncaught AssertionError: expected '<h4 style="color: #ccc;">test</h4>' to equal '<h4 style="color: #cccccc;">test</h4>'
      + expected - actual
      -<h4 style="color: #ccc;">test</h4>
      +<h4 style="color: #cccccc;">test</h4>

[gilbertwyw]

It would be useful as my current project requires "subject" to be of different language. But "subject" is not part of the template. I can make email-template package lookup different language folder that contain a meta data file. But this PR solves the problem much better.

[snow01]

@gilbertwyw - thanks !

Most of the time we need to customise subject with same data (variables) as the body - so it does make sense to use the same template system for both cases.

[niftylettuce]

Can you please rebase into one commit?

[ebourmalo]

I would really appreciate this feature as well :)

[snow01]

Okay, let me rebase and resubmit. Pull request kept waiting for months, and then I stopped following.

[ebourmalo]

@snow01 Any update on this :) ?

[snow01]

Hey @ebourmalo, @niftylettuce --

As there were some changes in upstream, created a new pull request: #164

Hope to see this getting merged soon.

Will discard this pull request.