Import class API from lua-users wiki
Initial version of ComputerCraft event API
Fix constructor based on example code.

I think the constructor needs to be written with an explicit self
parameter since it's written as an anonymous function.
Initial version of button library.
Fix syntax errors and API confusion.

Code block moved because it needs to use the Button class, which has to
be defined first.

Have to put the API name before calls to an API function.

Button callback is already provided in constructor, and it doesn't need
event details.
Fix syntax errors, add some debug output

Have to put the API name before calls to functions in that API.

List indexes are 1-based, not 0-based (grr!).

Have to use slightly odd syntax to iterate through handlers, otherwise I
get "attempt to call table" errors.