By using one letter for the path type before and one letter for path
type after, we can encode much more information than just the current
'M'/'A'/'R'. In particular, we can indicate new and resolved
conflicts. The color still encodes the same information as before. The
output looks a bit weird after many years of using `hg status`. It's a
bit more similar to the `git status -s` format with one letter for the
index and one with the working copy. Will we get used to it and find
it useful?