We can put the unsafe keyword as part of the function definition,
getting rid of the unsafe {} blocks in the functions themselves.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

The previous commit changed uwr_get_http_content_len() to return a u64
to allow for uploads larger than 4GiB, which now means this generates
compiler errors about type mismatches, expected usize got u64.

Cast the return value of uwr_get_http_content_len() to usize to match
that of TOTAL_RESPONSE_SENT.

(Making TOTAL_RESPONSE_SENT a u64 creates a larger trail of problems).

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Update the echo-request and upload-reflector examples for the new
uwr_http_add_header_content_type() and uwr_http_add_header_content_len()
functions.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This was used to specify the index of the response header being added,
starting at 0 and incrementing by one for each header.

Instead of having the programmer specify this, track it internally.

We add an extra check in luw_http_add_header() to make sure we aren't
trying to add more headers than we said with luw_http_init_headers(), if
we are, simply return.

This updates the API-C.md and the various examples and 'rusty' API
wrapper.

Suggested-by: Liam Crilly <liam@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

rusty is a thin wrapper over the generated libunit-wasm bindings to
provide a more native rust like interface.

This gets rid of all the casting and ugly string handling. It massively
reduces the amount of unsafe {} blocks needed, though some still are...

All in all this provides a nice code cleanup.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

libunit-wasm and example C and Rust WebAssembly modules for NGINX Unit.

Co-developed-by: Timo Stark <t.stark@nginx.com>
Co-developed-by: Liam Crilly <liam@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>