In output, indents should be a tab, not 4 spaces

[clbarnes]

Possibly contentious issue here, of course...

• Spaces appear commonly in file names, tabs do not, so there is less potential ambiguity
• Big output files mean lots of indents; why use 4x the characters?
• When parsing the output, startswith('\t')is a little nicer thanstartswith(" ")`

[clbarnes]

This could at least be partially resolved by documenting the output format.