Flatbuffers

* Rust soundness fixes to avoid the crate from bing labelled unsafe (7518).

* 20 Major releases in a row? Nope, we switched to a new
[versioning scheme](https://github.com/google/flatbuffers/wiki/Versioning)
that is based on date.

* Python supports fixed size arrays now (7529).

* Behavior change in how C++ object API uses `UnPackTo`. The original intent of
this was to reduce allocations by reusing an existing object to pack data
into. At some point, this logic started to merge the states of the two objects
instead of clearing the state of the packee. This change goes back to the
original intention, the packed object is cleared when getting data packed into
it (7527).

* Fixed a bug in C++ alignment that was using `sizeof()` instead of the intended
`AlignOf()` for structs (7520).

* C has an
[official Nuget package](https://www.nuget.org/packages/Google.FlatBuffers)
now (7496).

* Fix for `--keep-prefix` the was generating the wrong include statements for
C++ (7469). The bug was introduced in 2.0.7.

* Added the `Verifier::Options` option struct to allow specifying runtime
configuration settings for the verifier (7489). This allows to skip verifying
nested flatbuffers, a on-by-default change that was introduced in 2.0.7. This
deprecates the existing `Verifier` constructor, which may be removed in a
future version.

* Refactor of `tests/test.cpp` that lead to ~10% speedup in compilation of the
entire project (7487).

* This is the first version with an explicit change log, so all the previous
features will not be listed.

* Verifier now checks that buffers are at least the minimum size required to be
a flatbuffers (12 bytes). This includes nested flatbuffers, which previously
could be declared valid at size 0.

* Annotated binaries. Given a flatbuffer binary and a schema (or binary schema)
one can generate an annotated flatbuffer (.afb) to describe each byte in the
binary with schema metadata and value.

* First binary schema generator (Lua) to generate Lua code via a .bfbs file.
This is mostly an implementation detail of flatc internals, but will be slowly
applied to the other language generators.