More dynamic line ranges

[BlakeFreer]

Current line ranges can only support fixed line numbers, which means you cannot:

1. get "all lines after line 5". Currently, you could use lines=5-99999 but this is not robust and raises a warning.
2. Include the "last 10 lines" since you do not know these line numbers

Potential fixes could use syntax like:

1. lines=5-END or lines=5-
2. lines=-10-END following the Python slicing syntax where negative indices count from the end