src: refactor expression printing in code coverage report.

[Blebowski]

This MR has two changes to the way coverage items are printed in the HTML coverage report:

1. Line numbers are printed in the coverage item title, as opposed to only start of the code sample
2. Expressions are printed within single line. Comments are filtered. This simplifies drawing of LHS/RHS indicators and allows to draw them also for multi-line expressions. This format matches how some of the commercial tools show expressions in coverage tools.

Very long expressions don't fit into single line, but I think that can be tolerated.

[Blebowski]

This is now also ready for review. I ran the HTML validator over these changes too.

An example of "new format" in case of complex multi-line expressions:

vs. the old format:

[Blebowski]

Hi @nickg, do you think these changes can be merged ?