pre-merge commit
Merge branch 'master' of github.com:petehawkes/Nature-of-Code

Conflicts:
	Greenhouse/chp1_vectors/NOC_1_1_bouncingball_novectors/NOC_1_1_bouncingball_novectors.xcodeproj/project.xcworkspace/xcuserdata/pete.xcuserdatad/UserInterfaceState.xcuserstate
	Greenhouse/chp1_vectors/NOC_1_2_bouncingball_vectors/NOC_1_2_bouncingball_vectors.xcodeproj/project.xcworkspace/xcuserdata/pete.xcuserdatad/UserInterfaceState.xcuserstate
	Greenhouse/chp1_vectors/NOC_1_3_vector_subtraction/NOC_1_3_vector_subtraction.xcodeproj/project.xcworkspace/xcuserdata/pete.xcuserdatad/UserInterfaceState.xcuserstate
minor tweeks