Azure : Split build steps and only run docs for release or on linux
Azure : Split build steps and only run docs for release or on linux

Work-around for persistent mac doc build hang.

andrewkaufman/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,boberfly/gaffer,boberfly/gaffer,johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,hradec/gaffer,johnhaddon/gaffer,boberfly/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,boberfly/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,hradec/gaffer,johnhaddon/gaffer,hradec/gaffer,hradec/gaffer,ImageEngine/gaffer,GafferHQ/gaffer