Extends examples/keys program to also read individual

key/button press events.

Adds the evdev.Find() function, along with IsKeyboard, IsMouse

and IsJoystick. Find() can be used to return a list of
attached devices which qualify as the device represented by
the given constant. E.g.:

    keyboards, err := evdev.Find(evdev.Keyboard)

This returns a list of open devices which behave like a keyboard.
These may not actually be keyboards, but they support the events
that we expect from one: reporting key states and LED events.

When looking for Mouse devices, this may also return trackpads
and multi-touch screens. it is up to the host application to
figure out which one to actually use.

Adds an example program to demonstrate its use.

More code reformatting and additions of documentation.

Performs further refactoring.

Splits code up into more files. Combining all related
components for a given event type into its respective
file.

Adds a great deal of code comments, covering explanations
of what various types, methods and constants mean.

Renames Device.Supports() to Device.Test().

Given the multiple use cases this method has,
it is a better fit.

Fixes example programs to reflect this change.

Factors a lot of the API code out into separate files,

to keep the codebsae cleaner and easier to follow.

Applies code cleanup and refactoring to Device type.

Adds and fixes code comments.
Adds more Force feedback API implementation code to
the Device type.

Fixes example programs to reflect new changes.

Fixes examples/keys program.

Adds examples/exclusive program. It demomonstrates how to

obtain and release an exclusive lock on a device.

Adds examples/forcefeedback to demonstrate how to use the

various FF related API components.

This allows one to query for Force Feedback capabilities,
create and upload new effects and toggle their play state.