Wasm_of_ocaml runtime file

Fix C stubs to avoid returning void

Remove MirageOS 3 cross-compilation runes

MirageOS 4 is out since nearly a year, it's time to cleanup the leftover hacks
and workarounds. The opam file now contains a conflict with ocaml-freestanding
to avoid breakage for MirageOS 3.x users. [Since Mirage4 was released,
ocaml-freestanding is now known as ocaml-solo5.]

On 32 bits the overflow happens before than on 64 bits, use the
decimal representation of max_int to check.

The compiler will emit an error if an integer literal cannot be safely
represented on 32 bits arches.

> Since Dune 2.8, it’s possible to deactivate the systematic
> prepending of flags coming from ocamlc -config to the C compiler
> command line.
> The value true is the default for Dune 3.0.

https://dune.readthedocs.io/en/stable/dune-files.html#use-standard-c-and-cxx-flags

- With correct warn flags the MSVC compiler works

- With correct warn flags the MSVC compiler works

Bump to OCaml 4.08.0, remove bigarray-compat from dependency chain

add binding to C's memchr function.

switch to github actions

remove mirage-xen-posix cross-compilation rule (unneeded since mirage-xen 6.0.0)

also use a Makefile for freestanding builds (for tight control of CFLAGS), see
mirage/mirage-xen#23 for motivation and further details

update lower bound to dune 2.6

jsoo-conflicts-constraint: incompatible with jsoo < 3.5.0

update for jsoo#883

Compatibility with mirage+dune

Add :standard in c_flags on C stubs

dune-version: change version to 1.0

fix docstrings

add dune project name

because of this opam pin/install error:

#=== ERROR while compiling bigstringaf.0.5.0 ==================================#
# context 2.0.4 | openbsd/x86_64 | ocaml-system.4.07.1 | pinned(git+file:///home/madroach/src/bigstringaf#master#5fc35f1c)
# path ~/opam/system/.opam-switch/build/bigstringaf.0.5.0
# command ~/opam/system/bin/dune subst
# exit-code 1
# env-file ~/opam/log/bigstringaf-31496-dc6e87.env
# output-file ~/opam/log/bigstringaf-31496-dc6e87.out
### output ###
# Error: The project name is not defined, please add a (name <name>) field to your dune-project file.

Use Unsigned_long_val instead of Long_val in C stubs

Fix typo in "bounds checking" comment

port to dune

Fixing typos

travis: remove redundant entry from build matrix

Solving issue#26.
//Requres was written instead of //Requires, which was generating a "warning: free variables in primitive code "bigstringaf_memcmp_string" (/home/ziat/.opam/4.07.0/lib/bigstringaf/runtime.js:67)".