Added exceptions for open() and close() methods (issue #8)
Merge remote-tracking branch 'origin/master'

Conflicts:
	pi4j-core/src/main/java/com/pi4j/io/serial/Serial.java
	pi4j-core/src/main/java/com/pi4j/io/serial/SerialException.java
	pi4j-core/src/main/java/com/pi4j/io/serial/impl/SerialImpl.java