Use django's escape when using django templates

[quantum5]

Using pyjade.runtime.escape is fine in most situations, but when dealing with django-specific things, like lazy objects, or safe strings, pyjade.runtime.escape treats them as arbitrary objects, calling str on them.

For safe strings, this means they get escaped again. For lazy objects, it means they get forcefully converted into str even if they are unicode strings.

[kakulukia]

Since there are no updates to pyjade and its successor recently was deleted from pypi, I took the liberty to revive it: https://github.com/kakulukia/pypugjs

Version 5.0.1 has fixed the incompatibility with recent Django versions.
I'll be happy to merge this, when you resubmit the PR to my repo.