Move integration tests into src/tools/tests.

The integration tests use both libcretonne and libreader, so moving them avoids
the circular dev-dependency.

Also go back to building everything under src/tools/target to avoid rebuilding
the libraries when cargo is invoked in different subdirectories. This speeds up
test-all.sh quite a bit.

Finally, skip the pure debug build. We build "cargo test" and "cargo build
--release" which should cover everything we need.

src/libcretonne/Cargo.toml

@@ -11,8 +11,3 @@ build = "build.rs"
 [lib]
 name = "cretonne"
 path = "lib.rs"
-
-[dev-dependencies]
-cretonne-reader = { path = "../libreader" }
-
-[dependencies]