(similar to issue #10, but for the ed format)
For the ed diff format, when range of lines is a single line, the format differs from upstream.
Upstream compacts range "a,a" as just "a":
echo a > a
echo b > b
diff -e a b | head -1 # outputs "1c"
Whereas this implementation doesn't compact it:
cargo run -- -e a b # incorrectly outputs "1,1c"