.editorconfig

match: handle excludes using new differencematcher

As I've said on earlier patches, I'm hoping to use more composition of
simpler matchers instead of the single complex matcher we currently
have. This extracts a first new matcher that composes two other
matchers. It matches if the first matcher matches but the second does
not. As such, we can use it for excludes, which this patch also
does. We'll remove the now-unncessary code for excludes in the next
patch.

# See http://EditorConfig.org for the specification

root = true

[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true

[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true