[Feature] add new post content and topic subject to email notification

[cperinel]

When subscribed to a lot of topics, you may get a lot of email notifications for new entries.
It will be very usefull to have at least the content of the post, the name of the topic and the author to be able to follow mutliples topics more easily...

The problem will be the formatting of content of the email as it is now sended in text only and of course, a post content might have valuable HTML in it... see another features request for HTML emails ( #167 )

[DylannCordel]

Topic's name and post's author are already in email's body. Only post's content is missing.
Text formatting is bugged : a simple striptags does not correctly format the text content. For exemple :

<p>Hi</p><p>What a wonderfull app !<br />Have a look to <a href="https://github.com/hovel/pybbm">PyBBm</a> <img src="http://domain.ext/static/smilies/smile.png" alt=":-)" /></p>



<p>Bye !</p>

will be text formated in:

HiWhat a wonderfull app !Have a look to PyBBm



Bye !

Instead of

Hi

What a wonderfull app !
Have a look to PyBBm (https://github.com/hovel/pybbm) ;-) (image:http://domain.ext/static/smilies/smile.png)

Bye !

With smiley exemple, image's src seems to be a bad idea, but if this is a picture, it's usefull. We could define some more advanced rules depending on the image location :

• /static/ : we do not display the URL : only the Alt text
• other : (internal or external) we display the URL in addition to the alt text.