Write Graph Generator Utilities

[mzargham]

Starting reference cases from discussion with @decentralion

• line graph
• expanding tree
• converging tree
• sink (inward hub and spoke)
  -source (outward hub and spoke)

Use networkx it generate graphs consistent with python imlementation of pagerank for cred distribution analysis.

[mzargham]

I finished writing up the utilities [draft] will follow up with @BrianLitwin about unit testing before submitting a pull request

[teamdandelion]

@mzargham why did you close this issue? we haven't merged #21 yet.
typically we would write "Closes #21" in the PR description and then it would close this automatically once that code merges

[mzargham]

You can reopened it. i mis-interpreted your comment about pull request above as 'instead' rather than 'in addition' to. #learning