Rename intra_doc_link_resolution_failure lint to broken_intra_doc_links

[daira]

Fixes #279. This is dependent on updating Rust to a version that supports #![deny(broken_intra_doc_links)].

[codecov]

Codecov Report

Merging #280 into master will not change coverage.
The diff coverage is 84.91%.

@@           Coverage Diff           @@
##           master     #280   +/-   ##
=======================================
  Coverage   66.02%   66.02%           
=======================================
  Files         101      101           
  Lines       13214    13214           
=======================================
  Hits         8725     8725           
  Misses       4489     4489           

Impacted Files	Coverage Δ
bellman/src/lib.rs	32.60% <ø> (ø)
ff/src/lib.rs	39.18% <ø> (ø)
group/src/lib.rs	50.00% <ø> (ø)
jubjub/src/lib.rs	56.62% <ø> (ø)
zcash_primitives/src/note_encryption.rs	77.23% <ø> (ø)
zcash_primitives/src/prover.rs	30.76% <ø> (ø)
...imitives/src/test_vectors/pedersen_hash_vectors.rs	100.00% <ø> (ø)
zcash_proofs/src/lib.rs	69.69% <ø> (ø)
zcash_proofs/src/sapling/verifier.rs	0.00% <0.00%> (ø)
zcash_proofs/src/circuit/ecc.rs	84.25% <87.16%> (ø)
... and 7 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8b6c814...5e8a471. Read the comment docs.

[str4d]

PR is outdated due to #283, and we can't make this change until the new lint has stabilised, so let's make a new PR at that time.