put html attributes in quotes

heroku seems to be truncating whitespace,
which mangles HTML attrs if we don't quote them.
remove old example from front page
patch isuue 17 wrong element width
add GitHub auth
better logging / errors

use 400 if request is bad
fix error catching in cachedget

avoids turning 404/400 into 500
tweak error messages
fix gist url, disable ipynb fileext checking
catch render errors for raw urls
relax gist id regex

not all gists are ints
Merge pull request #25 from minrk/gisturls

tweaks to url checking

- update to be aware of new (and old and private) gist urls
- stop checking .ipynb file extension on raw urls
- avoid 500 errors on invalid notebooks at raw URLs
add missing return statements for /url[s]
interpret urls without prefix as http
add Book example
Merge pull request #26 from Carreau/example-front-page

add Book example
reenable cache

add require pylibmc, and read env variable to setup memcache
redirect 404s for "files/localfile" urls to a logical guess

This should let static-file serving work for some simple cases.
The files do not travel through nbviewer, it is a simple redirect.

if the first occurrence of `files/` is not the local-file shortcut, it will be wrong.
Merge pull request #28 from Carreau/cache

reenable cache
use newrelic
Merge pull request #27 from minrk/test

use newrelic