patch: add within-line color diff capacity The `diff' command usually writes deletion in red and insertions in green. This patch adds within-line colors, to highlight which part of the lines differ. Lines to compare are decided based on their similarity ratio, as computed by difflib SequenceMatcher, with an arbitrary threshold (0.7) to decide at which point two lines are considered entirely different (therefore no inline-diff required). The current implementation is kept behind an experimental flag in order to test the effect on performance. In order to activate it, set inline-color-diff to true in [experimental].