Offer my new and modified usr/app modifications and enhancements.

[ab1aw]

Modified the usr/app/gpioer/main.c (from benwei) to properly compile and execute within the master f-kernel branch.

Create a user app demonstration of a mechanism to work around the missing kernel support for passing an argument to a thread function.

Experimenting with user app examples demonstrating IPC among three (3) threads instead of two.

Modified ping-pong usr app to send incrementing message counter from ping thread to pong thread. Both threads display current counter value.

[slpbaby]

Should we put L4 User Manual link only instead of commit the pdf file? As I remember, git is not very good at handling binary file.