'make graph' enhancements

[smanders]

a previous 'make graph' enhancements issue https://github.com/smanders/externpro/issues/344 introduced graphPvtClean.sh.in, which removes private dependencies from the .dot file

this issue is to document additional enhancement(s)

[smanders]

it would be useful if there was some color introduced so it's more obvious which libraries are external libraries

• https://www.google.com/search?q=graphviz+colors
• https://renenyffenegger.ch/notes/tools/Graphviz/attributes/_color/index
• https://www.golinuxhub.com/2017/06/sed-insert-word-after-match-in-middle/

[smanders]

[smanders]

there may be future enhancements, but these will come in a new issue for now, completed with commit referenced above