Support inline text diffing

[jonnor]

Right now we emit one-line-per-change, basically without any formatting. This is OK for when there is no formatting capabilities, like when output is redirected to a file. However it is hard to see context, like grouping etc.

Might be better to basically render the new state of the graph FBP-like, but have red-colored parts, and green-colored for additions compared to the old state. Basically similar to git diff --word-diff=color

This renderer should support both consoles (using control characters), and HTML (using CSS). Thinking initially that CSS should be inlined. Though should possibly use semantic class-names from the get-go.