Switch to relative paths in Cargo.toml

See the discussion here for an explanation of how this works:

rust-lang/cargo#937

We also remove the "exclude" line, since it doesn't work, and it's
about to become unnecessary once the bug is fixed.

Cargo.toml

@@ -12,10 +12,6 @@ repository = "https://github.com/emk/rust-uchardet"
 readme = "README.md"
 keywords = ["encoding", "text", "i18n"]
 
-# Make sure we don't package this in our build, which will badly confuse
-# crates.io and Cargo.  See https://github.com/rust-lang/cargo/issues/937
-# for discussion.
-exclude = ["uchardet-sys"]
-
-[dependencies]
-uchardet-sys = "~0.0.2"
+[dependencies.uchardet-sys]
+path = "uchardet-sys"
+version = "~0.0.2"