rethink the state space for uart io read test. updat comments and test case names.
refactoring uart io write test case, two cases left.
uart io write test cases refactored. allocate test object on stack.
clean commented code.
adding config class, refactoring ctor & factory method.
uartex handle factory create refactored. now the factory method is configration based.
add msp class.
dma factory class removed. This responsibility should be moved to msp class.
UARTEX handle factory class removed. The responsibility should be moved to msp.
uart io handle refactored to be uart_device.
adding test to uart device open, some design problems and being frustrated.
Merge pull request #11 from matianfu/master

redesigned i/o