v0.7.0

CHANGES:

• CPU feature detection (AESNI, SSE3, PCLMULQ) at runtime instead of compile
  time (#53 @Julow, fixed MirageOS support #61, review by @hannesm)
  performance hit up to 5%
• Revise entropy collection (#64 @hannesm review by @dinosaure @cfcs)
  mirage-crypto-entropy has been folded into mirage-crypto-rng.{unix,lwt,mirage}
  • the RNG is no longer fork() safe, if you use fork in your code, be sure to
    reseed the RNG in the child process
  • on Unix and Lwt, the used RNG is Fortuna, seeded by getrandom(),
    rdrand/rdseed, and whirlwind
  • Mirage_crypto_rng_lwt does entropy collection for Lwt applications
  • entropy collection is now similar to FreeBSD:
    • rdrand/rdseed is executed in a separate task (by default every second)
    • on Unix, getrandom() is executed in another separate task (by default
      every 10 seconds)
    • on every enter of the Lwt event loop, some bits of rdtsc are collected
      (rdrand/rdseed is not on each even loop enter anymore)
  • Fortuna only uses entropy pools if the given period is exhausted (defaults
    to 1s), and the pool size exceeds 64 bytes
  • The unseeded generator exception prints instructions how to seed the RNG
• 32 bit support (for ghash), requested by @TImada in #60, #65 @hannesm
• use Eqaf_cstruct.find_uint8 instead of Cs.ct_find_uint8 (#52 @dinosaure)
• add (:standard) in C flags to allow cross-compilation #47 @samoht
• Mirage_crypto.Uncommon: remove several functions (Cs.create, Option),
  requires OCaml 4.08 (#49 #51 @hannesm)
• remove ocplib-endian dependency, use Bytes directly (since 4.07) #51 @hannesm
• bitfn.h cleanup (#56 #58 @hannesm)
• fix build if opam is not available (#66 @hannesm)
• update test.yml GitHub actions (#44 #57 @imbsky)
• Travis CI for arm64 (#55 @hannesm)