tendermint-rs: Initial JSONRPC over HTTP client

Adds a hyper-based HTTP client for making JSONRPC requests.

Uses a slightly old version of hyper (0.10) which does not yet depend on
futures/tokio, the idea being updating to a fully async version should
be possible in the future.

Adds an integration test which can be used against gaiad locally. This
isn't run in CI (yet) but it is built in CI at least to ensure changes
still allow it to compile.

.circleci/config.yml

@@ -26,7 +26,7 @@ jobs:
           cargo build --features=yubihsm
           cargo build --features=ledgertm
           cargo build --features=yubihsm,ledgertm,softsign
-          cd tendermint-rs && cargo build --no-default-features
+          cd tendermint-rs && cargo build --no-default-features && cargo build --features=integration --tests
     - run:
         name: build --release
         command: |
@@ -40,7 +40,7 @@ jobs:
           rustc --version
           cargo --version
           cargo test --all --all-features -- --test-threads 1
-          cd tendermint-rs && cargo test --release --all-features
+          cd tendermint-rs && cargo test --release --features=amino-types,rpc,secret-connection
     - run:
         name: audit
         command: |