async_enqueue() is a wrapper over the async_enqueue_buffer() call
to AudioServer. This allows users to asyncronously enqueue audio
samples, when the program requires non-blocking audio streaming.
This also makes ClientConnection use east-const everywhere.
This changes client methods so that they return the IPC response's
return value directly - instead of the response struct - for IPC
methods which only have a single return value.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
