Include space and backspace in default set of slide movement keys
Have main slot take up full slide

This lets you do things like this and get the expected result:

```
slide do
  background yellow
end
```
Add hook for when a slide is hiding

Found for my fancier slides I needed to do some cleanup (stop
animations, etc.) This hook was the clearest way I could see to plumb
that through.
Let image calls pass arguments along

Needed this to do some placement on initialize with them. Could have
grabbed the returned element and set it directly, but wanted the tidier
feel
Allow passing block to code and demo

This will get passed the resulting app so you can do things like wire up
additional closing commands on an app without having to modify it's
source directly.
Merge pull request #11 from PragTob/other_next_previous_keys

Include space and backspace in default set of slide movement keys
Merge pull request #12 from PragTob/make_slides_full_window

Have main slot take up full slide
Merge pull request #14 from PragTob/image_arguments

Let image calls pass arguments along
Better naming on slide change hook
Merge pull request #13 from PragTob/hiding

Add hook for when a slide is hiding
Variable rename
Keep Ctrl+w as default quit key on demo code
Merge pull request #15 from PragTob/code_and_demo_hook

Allow passing block to code and demo
Support passing startup options for main Shoes.app call

Right now these can be called from anywhere, but are additive to ease that pain
Move default startup options to configuration