Add section for Kernel tuning in Postgres performance page

About vm.*dirty* parameters and swap.
Rename whole documentation to archlinux for consistency

At a couple of places Arch-Linux or even Arch Linux was used. The
new way of naming this distribution is an abuse in the docs though
as the real name is really "Arch Linux" as mentioned in the front
page of this project.
Remove direct naming of this blog root URL

Better to use "/" instead of "http://michael.otacoo.com/", the root
URL being then generated by jekyll itself.
Fix warnings found in jekyll 2.4