Add a ureq version of esplora module

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

src/error.rs

@@ -130,7 +130,7 @@ pub enum Error {
     Electrum(electrum_client::Error),
     #[cfg(feature = "esplora")]
     /// Esplora client error
-    Esplora(crate::blockchain::esplora::EsploraError),
+    Esplora(Box<crate::blockchain::esplora::EsploraError>),
     #[cfg(feature = "compact_filters")]
     /// Compact filters client error)
     CompactFilters(crate::blockchain::compact_filters::CompactFiltersError),
@@ -190,8 +190,6 @@ impl_error!(bitcoin::util::psbt::PsbtParseError, PsbtParse);
 
 #[cfg(feature = "electrum")]
 impl_error!(electrum_client::Error, Electrum);
-#[cfg(feature = "esplora")]
-impl_error!(crate::blockchain::esplora::EsploraError, Esplora);
 #[cfg(feature = "key-value-db")]
 impl_error!(sled::Error, Sled);
 #[cfg(feature = "rpc")]
@@ -216,3 +214,10 @@ impl From<crate::wallet::verify::VerifyError> for Error {
         }
     }
 }
+
+#[cfg(feature = "esplora")]
+impl From<crate::blockchain::esplora::EsploraError> for Error {
+    fn from(other: crate::blockchain::esplora::EsploraError) -> Self {
+        Error::Esplora(Box::new(other))
+    }
+}