Doesn't build on Rust nightly

[frewsxcv]

   Compiling brotli v0.3.19 (file:///Users/coreyf/Development/rust/brotli-rs)
src/lib.rs:686:18: 686:33 error: const indexing is an unstable feature
src/lib.rs:686              sum += 32 >> code_lengths[i];
                                         ^~~~~~~~~~~~~~~
src/lib.rs:686:18: 686:33 help: in Nightly builds, add `#![feature(const_indexing)]` to the crate attributes to enable
src/lib.rs:1512:10: 1512:60 error: const indexing is an unstable feature
src/lib.rs:1512                 1 << BROTLI_DICTIONARY_SIZE_BITS_BY_LENGTH[copy_length]
                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/lib.rs:1512:10: 1512:60 help: in Nightly builds, add `#![feature(const_indexing)]` to the crate attributes to enable
src/lib.rs:1518:34: 1518:84 error: const indexing is an unstable feature
src/lib.rs:1518             let transform_id = word_id >> BROTLI_DICTIONARY_SIZE_BITS_BY_LENGTH[copy_length];
                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/lib.rs:1518:34: 1518:84 help: in Nightly builds, add `#![feature(const_indexing)]` to the crate attributes to enable
error: aborting due to 3 previous errors
Could not compile `brotli`.

To learn more, run the command again with --verbose.

coreyf@frewbook-pro ~/D/r/brotli-rs (master) [101]> rustc -Vv
rustc 1.6.0-nightly (d49e36552 2015-12-05)
binary: rustc
commit-hash: d49e365528e026df6f56fe5eb001e81e2383fbf5
commit-date: 2015-12-05
host: x86_64-apple-darwin
release: 1.6.0-nightly

[frewsxcv]

Related issue: rust-lang/rust#29947

[ende76]

Thanks, Corey, for alerting me to this. I do believe that it's really an issue in the nightly change rather than in my code, but the workaround (same as @debris in debris/tiny-keccak@591d611 )was simple enough to implement.