v5.0.0

CHANGES:

Security: This release tightens bounds checks to ensure
that data outside a given view (but still inside the underlying
buffer) cannot be accessed.

• sub does more checks (#244 #245 @hannesm @talex5 review by @dinosaure)
• add_len and set_len are now deprecated and will be removed
  in a future release. (#251 @hannesm)
• do not add user-provided data for bounds checks
  (#253 @hannesm, report and review by @talex5)
• improve CI to add fuzzing (#255 #252 @avsm @yomimono @talex5)

Remove Unix dependency: cstruct now uses the new bigarray-compat
library instead of Bigarray directly, to avoid a dependency on Unix
when using OCaml compilers less than 4.06.0. This will break downstream
libraries that do not have a direct dependency on Bigarray. Simply
fix it in your library by adding a bigarray dependency in your dune
file. (#247 @TheLortex)

Capability module: To improve the safety of future code with stronger type
checking, this release introduces a new Cstruct_cap module which makes the
underlying Cstruct an abstract type instead of a record. In return for this
extra abstraction, the module can enforce read-only, write only, and read/write
buffers by tracking them as phantom type variables. Although this library
shares an implementation internally with classic Cstruct, it is a significant
revision and so we will be gradually migrating to it. Feedback on it is
welcome! (#237 @dinosaure and many excited reviewers)

Ppx compare functions: A new compare_X function is generated for
cenum declarations. This respects custom ids supplied in the cenum
declaration and so is more robust than polymorphic compare (#248 @emillon)

The CI has also been switched over to both Azure Pipelines and Drone in
addition to Travis, and as a result the tests all run on Windows, macOS,
various Linux distributions, on x86 and arm64 machines, and runs AFL
fuzz tests on the Drone cloud (#255 @avsm).