Implement Arduino's random() functions, issue #215

Also, when https://github.com/spark/core-communication-lib/pull/25
is merged, then the user will automatically have a secure random
seed after handshaking with the Spark Cloud.
unit tests + factored out random() to separate files
include in spark_wiring.h for new random functions.
(And integration test case for that bug.)
allow apps to use c++11 features also
moved setting gnu++11 flag to correct location
unwanted change.
half-cut test removed - function covered by xx_range_values_are_within_range.
Merge branch 'master' into feature/random

Conflicts:
	inc/spark_wiring.h
	tests/unit/makefile
Merge branch 'feature/random'