Add last line of expression to debug stack frames, set display line number to begin/end as appropriate

[ronhitchens]

The MarkLogic debug API breaks at both begin and end of expressions. It would be far more intuitive for users to display the editor cursor on either the first or last line of an expression as appropriate, since expressions can span many lines to include subexpresisons.

The stack returned from dgb:stack only includes the first line of the expression. But it should be possible programmatically to determine the last line of an expression.

[ronhitchens]

Code is in place now to set the last line on the returned stack frames. But the last line number is not being used yet, because the way breakpoints are currently set effectively defeats the purpose. It is not usually practical to select expressions that wrap around other expressions across multiple lines.

I created Issue #29 to provide that capability. Until then, I'm placing this in the Icebox. If/when #29 is implemented, I'll revisit this to add the breakpoint display mechanism to position to the beginning or end of an expression as appropriate.

[ronhitchens]

Depends on #29.