Add support for custom params in theme demos

[bep]

See:

https://github.com/spf13/HugoBasicExample

Also see #3 for how-to-build-this-site.

This is the site used for all the theme demos. In the config.toml there are some added params to get the themes up and running.

But there are more custom params that could be added so the different themes get the best possible presentation.

Casper is one, that takes a "big image" as site param.

We need some kind of config rewriting with a list of param addons (we do not want to commit this to the example site):

• Assume that we can have one config for all themes (they will ignore the one they don't know about)
• Use Casper as "proof of concept": Add the front page image on http://gohugo.io/ as a "splash image"

Then we can add the necessary params one by one later.

[bep]

Fixed, see https://github.com/spf13/hugoThemesSite