Add checks for doxygen and inkscape executables
Add checks for doxygen and inkscape executables

ivanimanishi/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,hradec/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,hradec/gaffer,chippey/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,boberfly/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,boberfly/gaffer,lucienfostier/gaffer,ivanimanishi/gaffer,boberfly/gaffer,chippey/gaffer,hradec/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,hradec/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,boberfly/gaffer,GafferHQ/gaffer,chippey/gaffer,andrewkaufman/gaffer,chippey/gaffer,lucienfostier/gaffer,hradec/gaffer