Allow usage of [[page_cu]] in css class names

[marbetschar]

This fixes #522 by allowing the usage of the current page number within a css class name. By using this we are allowed to apply different styling depending on which page we are.

[spipu]

Thanks !
The MR #551 fix the travis pb. Once it has been fixed, could you rebase your branch from the master to fix it, and also add an enty on the changelog file, and add an example ? thanks !

[marbetschar]

@spipu I no longer have access to the corresponding use case in order to rebase/test etc. the fix. Feel free to copy & paste the few lines of code into master and reject this pull request.

[spipu]

ok. Just confirm me how it was working : just using class="content-[[page_cu]]" in the html and adding the good css definition ?

[marbetschar]

exactly.

[spipu]

example added

[spipu]

42836b8

[simplygest]

Is it possible to also allow usage of [[page_nb]] in CSS class names? This will allow us to hide/show page content depending on the number of pages.