put more meaning into the edges' representation

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>
Improve node layout

Limit each node to one line in the dot file

Choose better formatting to distinguish between various types of
nodes: phony/real, created/existing, directly called, precious etc

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>
a suggestion for stem type

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>
Profile option: -u/--update-time -> -P/--profiling

-P/--profile is a better name for profiling option
Profile option will accept parameter for ouput format

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>