Bump minimum Rust version and change policy

.travis.yml

@@ -1,6 +1,6 @@
 language: rust
 rust:
-  - 1.21.0
+  - 1.25.0
   - stable
   - nightly
 cache: cargo

CHANGELOG.md

@@ -2,6 +2,19 @@
 
 ## Unreleased
 
+### Breaking Changes
+
+* Bump the minimum supported Rust version and change the Rust version policy.
+
+  From now on, `xmlrpc` will adopt the same policy as [tokio] (on which we
+  depend): We will support the current Rust version and the 2 releases prior to
+  that (which currently means that we support 1.25.0+).
+
+  Bumping the required Rust version is no longer considered a breaking change as
+  long as the latest 3 versions are still supported.
+
+[tokio]: https://github.com/tokio-rs/tokio
+
 ### New Features
 
 * Add `Request::new_multicall` for easier execution of multiple calls via `system.multicall`

README.md

@@ -8,6 +8,13 @@ This crate provides a simple implementation of the [XML-RPC specification](http:
 
 Please refer to the [changelog](CHANGELOG.md) to see what changed in the last releases.
 
+## Rust support
+
+This crate uses the same Rust versioning policy as [tokio]: It supports the last
+3 stable Rust releases. Increasing the minimum supported version is not
+considered a breaking change as long as the latest 3 versions are still
+supported.
+
 ## Usage
 
 Start by adding an entry to your `Cargo.toml`:
@@ -24,3 +31,5 @@ extern crate xmlrpc;
 ```
 
 See [`examples/client.rs`](examples/client.rs) for a small example which connects to a running Python XML-RPC server and calls a method. A more elaborate example that demonstrates how to implement a custom `Transport` to set a cookie header is provided in [`examples/custom-header.rs`](examples/custom-header.rs).
+
+[tokio]: https://github.com/tokio-rs/tokio