Move Graph Comparison section to immediately after the sections defining graphs and terms

[afs]

The graph comparison section is important so put it immediately after the sections defining terms.

Suggetsed new order:

3. RDF Graphs
   3.1 Triples
   3.2 IRIs
   3.3 Literals
   3.4 Blank Nodes
   3.5 Triple Terms
   3.6 Graph Comparison
   3.7 Initial Text Direction
   3.8 Replacing Blank Nodes with IRIs

[hartig]

With PR #140 merged, this change can be implemented now.

[afs]

This is still an issue marker in that section but the issue is now closed.
I will remove the issue note in the PR - it can be put back if needed.

[gkellogg]

Best thing is for PRs to remove issue markers they resolve.

[hartig]

It appears that the issue marker wasn't present in the first place in the branch of my PR #140. I guess I created that branch from main before the PR that added all the issue markers was merged.

I agree that removing the issue marker should be part of the PR that addresses the corresponding issue.

[afs]

No problem - I'll remove it.

As we mostly use rebase-and-merge, the boundaries of PRs isn't recorded long term in the git history.
Which is good for small PRs because they end up as x2 log entries.