The `Blockchain` implementation for connecting to an Esplora instance is
currently based on `reqwest`. Some users may not wish to use reqwest.
`ureq` is a simple HTTP client (no async) that is useful when `reqwest`
is not suitable.
- Move `esplora.rs` -> `esplora/reqwest.rs`
- Add an implementation based on the `reqwest` esplora code but using `ureq`
- Add feature flags and conditional includes to re-export everything to
the `esplora` module so we don't effect the rest of the code base.
- Remove the forced dependency on `tokio`.
- Make esplora independent of async-interface
- Depend on local version of macros crate
- Also upgrade reqwest
- Switch to `tokio::runtime::Builder::new_single_thread()` because
`tokio::runtime::Runtime::new()` changed it's behavior to create a
multithreaded runtime.
- `enable_all` enables time and io resource drivers as explained
[here](https://docs.rs/tokio/0.2.24/tokio/runtime/index.html#resource-drivers)
The procedural macro `#[maybe_async]` makes a method or every method of a trait
"async" whenever the target_arch is `wasm32`, and leaves them untouched on
every other platform.
The macro `maybe_await!($e:expr)` can be used to call `maybe_async` methods on
multi-platform code: it expands to `$e` on non-wasm32 platforms and to
`$e.await` on wasm32.
The macro `await_or_block!($e:expr)` can be used to contain async code as much
as possible: it expands to `tokio::runtime::Runtime::new().unwrap().block_on($e)`
on non-wasm32 platforms, and to `$e.await` on wasm32.
