Add terminal.png

This allows running examples using `cargo run --example example_name` with a
recent Cargo.

The non-console examples worked before as well, but whenever you call
`Console::init_root` it either expects a font to be set or looks for
`terminal.png` in the current directory.

We're relying on the fallback to keep the examples more focused.
Merge pull request #34 from tomassedovic/add-default-font

Add terminal.png