piros/tor: Code added to Tor to support PIR-based onion service descriptor lookups @ 1442e818b67561c810c5d18894e29c57f8fdbbb0

Nick Mathewson 1442e818b6 Merge remote-tracking branch 'isis-github/bug26106'		%!s(int64=6) %!d(string=hai) anos
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digests	af182d4ab5 rust: Add crypto crate and implement Rust wrappers for SHA2 code.	%!s(int64=6) %!d(string=hai) anos
rand	9988882c63 rust: Move rand crate into crypto parent crate.	%!s(int64=6) %!d(string=hai) anos
Cargo.toml	4d349c6a61 rust: Update rand_core dependency to 0.2.0-pre.0.	%!s(int64=6) %!d(string=hai) anos
lib.rs	4c21d41407 rust: Export digests subcrate from our crypto crate.	%!s(int64=6) %!d(string=hai) anos