Update DueTimer.h

Added Arm detection and support for the dynamic clock picking.
Added getFrequency(), getPeriod(), and protected var to store those values
Update DueTimer.h
Merge branch 'enchancements' of https://github.com/ivanseidel/DueTimer into enchancements

Conflicts:
	DueTimer/DueTimer.h
Update DueTimer.cpp

Added Clock picker.
Merge branch 'enchancements' of https://github.com/ivanseidel/DueTimer into enchancements

Conflicts:
	DueTimer/DueTimer.h
Merge branch 'enchancements' of https://github.com/ivanseidel/DueTimer into enchancements

Conflicts:
	DueTimer/DueTimer.cpp
Added pragma message to warn if included wrongly
fixed bugs
added getAvaliable()
added AvaliableTimer example
Update README.textile
Added new Example
Merge pull request #5 from ivanseidel/enchancements

V1.2 Released