etime: added split to StandardILPGenerator.

include/otawa/etime/AbstractTimeBuilder.h

include/otawa/etime/StandardILPGenerator.h

include/otawa/etime/features.h

src/etime/AbstractTimeBuilder.cpp

src/etime/EdgeTimeBuilder.cpp

src/etime/StandardILPGenerator.cpp

src/etime/StandardXGraphBuilder.cpp

src/etime/hook.cpp