Remove IntoBuf/FromBuf (#288)

As consequence Buf::collect is removed as well, which is replaced with `Buf::into_bytes`. The advantage of `Buf::into_bytes` is that it can be optimized in cases where converting a `T: Buf` into a `Bytes` instance is efficient.

ci/azure-cross-compile.yml

@@ -37,6 +37,7 @@ jobs:
     - script: |
         git clone https://github.com/rust-embedded/cross.git
         cd cross
+        git reset --hard fb1cb1d7288151f4349f1cb4c990e0e2281764da #Is broken after this commit (images are not uploaded to new docker hub)
         git apply ../ci/cross-patch
         cargo install --path .
         rm -rf cross

ci/cross-patch

@@ -1,5 +1,5 @@
-diff --git a/src/docker.rs b/src/docker.rs
-index 1525b87..5c9cd54 100644
+diff --git a/src/docker.rs b/src/docker.rs
+index 6ea745d..15fef81 100644
 --- a/src/docker.rs
 +++ b/src/docker.rs
 @@ -62,7 +62,7 @@ pub fn register(target: &Target, verbose: bool) -> Result<()> {
@@ -12,8 +12,8 @@ index 1525b87..5c9cd54 100644
          .args(&["sh", "-c", cmd])
          .run(verbose)
 @@ -160,7 +160,7 @@ pub fn run(target: &Target,
-         .args(&["-v", &format!("{}:/rust:ro", sysroot.display())])
-         .args(&["-v", &format!("{}:/target", target_dir.display())])
+         .args(&["-v", &format!("{}:/rust:Z,ro", sysroot.display())])
+         .args(&["-v", &format!("{}:/target:Z", target_dir.display())])
          .args(&["-w", "/project"])
 -        .args(&["-it", &image(toml, target)?])
 +        .args(&["-i", &image(toml, target)?])