ENH: Add basic experiment

Closes #151. @rkmaddox ready for review/merge.
On my system, the output from this line is 

```
Presses:
[]
```

So aside from my preference for the future-compatible `str.format()` syntax instead of `%s` syntax, it's a little confusing that the button press capturing doesn't start until after the user has pressed the button.  In other words, the button press they are prompted for is getting swallowed by `ec.screen_prompt`, so unless the user presses the button additional times during the 1-second beep, they will always get this confusing output.