**Secure Streams** support in lws was introduced a couple of years ago, it's a
higher-level interface to lws `wsi`-level apis that simplifies connectivity by
segregating connection policy like protocol and endpoint information into a
separate [JSON policy file](./minimal-examples/client/hello_world/example-policy.json), and just having the [code deal with payloads](./minimal-examples/clients/hello_world/hello_world-ss.c); as many
details of the wire protocol as possible are hidden or moved to the policy, so
user code is almost identical even if the wire protocol changes.
The user code just asks to create a SS by "streamtype name", it is created
according to the details (protocol, endpoint, etc) under the same name in the
policy.
Key policy entries like endpoint can contain `${metadata-name}` string
substitutions to handle runtime adaptations via metadata. h1, h2, ws and mqtt
are supported.
As a layer on top of the `wsi` apis, SS provides a higher-level way to access
the existing wsi-level capabilities, both kinds of API will remain supported.
Secure Streams are longer-lived than a single wsi, so an SS can coordinate
retries by itself. SS-based user code is typically significantly smaller and
more maintainable than wsi layer.
In main branch I have moved the older examples into `./minimal-examples-lowlevel`
and am starting to port more cases from there into SS-based examples.
### Comparison between wsi and SS level lws usage
|Feature|"low-level" wsi way|Secure Streams way|
|---|---|---|
|Create context|code|same|
|Loop support, sul scheduler|default, event libs|same|
The serialized SS can also travel over generic transports like UART, an [example
is provided implementing the Binance example on an RPi Pico](./minimal-examples/embedded/pico/pico-sspc-binance) with a UART transport
to a [UART transport SS proxy](./minimal-examples/ssproxy/ssproxy-custom-transport-uart), where the pico itself has no network stack, tls, compression or
wss stack, but can send and receive to and from the endpoint as if it did.
The optional `lws_trasport_mux` is used to interpose between the UART transport
and the SSPC layer, allowing a single pipe to carry many separate SS connections.
The user SS code is identical however it is transported, muxed and fulfilled.
