Update gpio.c

Added check to error.
Resized variables
Clean.
Update gpio.h

update function prototipies.
Update example_write.c

Uodate example.
Update example_read.c
Update example_write.c
Update gpio.h

added stdlib.h to use malloc and itoa
Update gpio.h
Update gpio.c

Added function to check if pin exist and resize variables
Update gpio.h

Define some costants
Update gpio.c
Update example_write.c

fixed while
Merge pull request #3 from dlion/master

Code refactored; dlion++