cargo-c will produce a pkg-config file making it easier to statically
link plugins.
Also add 'static' features for plugins depending on < 1.14 as this is the
minimal required version to use static linking because of ABI changes in
core.
This mutex is actually only ever used from a single thread, so use
AtomicRefCell instead. It provides the guarantees of a mutex but panics
instead of blocking.
There is no way to dynamically ask Cargo to build static or dynamic lib
so we have to build both and pick the one we care when doing the meson
processing.
Fix#88
This moves to Rusoto 0.43, which has moved from futures to async/.await.
As a result, we implement a utility function to convert the
async/streaming bits to blocking operations backed by a tokio runtime.
In the process, we also need to restructure s3sink a little, so that the
client is now part of the started state (like it is for s3src). This is
a better model than a separate client, as it reflects the condition that
the client is only available in the started state.
