Allow configuring indentation

[rimas-kudelis]

It's currently very impractical to migrate between ufonormalizer and psfnormalize, because ufonormalizer uses tabs for indentation, whereas psfnormalizer uses space characters by default.

It would be great if at least this aspect of ufonormalizer (although maybe others as well) could be configured via command-line arguments and/or lib.plist entries.

The need for minimized diffs in version control does not mean that different projects/authors can't have different preferences.

[benkiel]

PR welcome on this, would do it as command-line for sure, and a plist key optionally