build is commonly used with CMake (default build dir in VS code)
.cache is used by clangd

CMake 3.8 provides the slightly cooler compile feature cxx_std_11, but
we are on 3.7 for now.

However, target_link_libraries also supports link flags, which is
available for declared CMake version 3.7

Asio does not require Boost.
Bosot.Asio requires Boost.System and optionally Boost.Regex.
The examples require Boost headers and Boost.Filesystem.
The CMake targets pull in their dependencies recursively, no need to
explicitly link the examples to Boost.System.
Boost.Thread should not be neede, according to the docs.

Wrapped async_write calls in a strand since these calls might not be safe to call outside of the context runners if tls is used

There was a possible work-around - add the Transfer-Encoding: "chunked" header - but this is not correct as SSE and chunked are two different things.