pelican.conf.py: Enable DELETE_OUTPUT_DIRECTORY

We had some issues with output/ being unclean on some devs' copies
and it caused confusion when trying to reproduce bugs some devs
were experiencing.

This ensures output/ is always cleaned before building.
Add new post about playing with hardware-accelerated AES
Merge pull request #40 from alanorth/aesni

Add new post about playing with hardware-accelerated AES
Merge pull request #38 from alanorth/clean-output

pelican.conf.py: Enable DELETE_OUTPUT_DIRECTORY