PICrouter v1.12.0 release.

Deleted the USB callback functions and global variables in picrouter.c.
Added header and source file(usb_callback.h/.c) for the USB callback functions.
Fixed the initialization of the host name.
Recompiled.
Added the usb_callback.h/.c in the project.
Added unused #include line.
Deleted some commented line.
Renewed
Updated README.