[MUX] Cleanup function has correct prototype.
[INTERFACE] Fixed a bug in the systimer interface definition.
[INTERFACE] SPI - Corrected SPI transfer method prototype.
[SYSCALL] Added some POSIX errno definitions.
[SYSCALL] open - Provided POSIX compliant open() syscall.
[SYSCALL] close - Provided POSIX compliant close() syscall.
[SYSCALL] read - Provided POSIX compliant read() syscall.
[SYSCALL] write - Provided POSIX compliant write() syscall.
[SYSCALL] lseek - Provided POSIX compliant lseek() syscall.
[SYSCALL] POSIX - Default syscall handler sets errno in POSIX compliant way.
[SYSCALL] POSIX - Handle errno correctly.