header p CSS, homepage header

the header in the homepage has h1 and p, without h2 (which doesn't
make sense - h2 is for the main)
simple template and post template, with CSS

are decent. :-)
the header in post template is no longer a h1

it's free to be as given in the website.py (with p's, h2's...)

To Do:
* index template (and relative CSS)
* content for everything except about page
category is an attribute of the PostIndexTemplate class

this allows
* to leave the formatting (e.g., modifications of the title) in
the template (where it's supposed to be)
* to have a reference to the CSS file in the template! otherwise
the template for the "general" index is at "../static/..." and
the template for the "category" index is at "../../static/..."
templates, basically

index template is is a better shape. a couple of "posts" to check
how things work.

the title is no longer modified in post class
title with |striptags

title is plain text; this is done with the Jinja2 filter
striptags()
link to index of all posts

in index template, using if category