msg.{c,h}: fast low-level msgpack encoding

== Compiling ==

  gcc -c -O2 [-flto] msg.c
  clang -c -O2 [-flto] msg.c
  tcc -c msg.c
  cl.exe /c /O2 msg.c

In most cases you can just drop the .c file straight into your codebase/build
system. LTO is advised to avoid dead code and enable more efficient calls
including potential inlining.

== Compiler compatibility ==

- Any reasonable GCC
- Any reasonable Clang
- Any reasonable MSVC
- TinyCC
- Probably almost all others; this is very portable code

Note that GCC and Clang will generally give the best-performing output.

Once the .c file is built, the public header can be consumed by virtually any C
or C++ compiler, as well as probably most half-decent FFIs.

Note that the .c source file is not C++-compatible, only the header is. The
source file relies on union type-punning, which is well-defined in C but
undefined behaviour in C++.

== API Usage ==

See documentation comments in msg.h for a basic idea. Note that this library is
very low-level and probably best suited use with some sort of metaprogramming/
code-generation, or bindings to a higher-level langauge.

== OS Compatibility ==

- All.
- Seriously, this library doesn’t even use libc.

== Architecture compatibility ==

- The library is primarily optimised for 32- and 64-bit x86, with some
  consideration towards ARM
- It should however work on virtually all architectures since it’s extremely
  simple portable C code that doesn’t do many tricks

== Copyright ==

The source file and header both fall under the ISC licence — read the notices in
both of the files for specifics.

Thanks, and have fun!
- Michael Smith <mikesmiffy128@gmail.com>