Async: reserved keyword

[theduke]

In the 2018 edition, and already on nightly, async is a reserved word.

So while reqwest still compiles because it is compiled as 2015 edition, the async async module can't be used without a compilation error for reserved keyword usage.

This can be circumvented with a raw identifier (eg: use reqwest::r#async as asyn or use reqwest::r#async::Client), but this is obviously really awkward.

The async module will have to be renamed, which will force a version bump so it's a shame we didn't notice before 0.9 but what can you do.

It would be nice to get this out rather soon though, because nightly already has edition 2018 enabled by default when creating a new crate.

[seanmonstar]

As you mentioned, the module can be referenced via "raw identifiers", r#async. It is more awkward than normal imports, that's true.

A new naming scheme would be needed to differentiate between the blocking and async APIs.

[Arnavion]

(Previously discussed in #310 )

[NilSet]

Opened #408 to address this. Let me know if you have qualms about the name I chose.

[seanmonstar]

This was resolved by making the async API the default, and adding a blocking module.