Reproducible Build

With the same rust version and docker image, capsule build is mostly reproducible, with the following caveats:

• The absolute path of $CARGO_HOME/$PWD or some other directories may end up in the binary in e.g. panic messages. Use strings to check for file paths in the binary. Use --remap-path-prefix to replace these paths, e.g.:

  $ RUSTFLAGS="--remap-path-prefix=$HOME=~ --remap-path-prefix=$PWD=" capsule build --release

  (Capsule 0.10.1 will add this automatically. You can still use RUSTFLAGS to remap other paths.)