Bump version to v2.8.0-beta.1

There are so many significant changes,
that it makes sense to release a beta version
before doing a full release.

However, this beta release is likely higher quality than v2.7,
simply because it has gone through so many refactorings and fixes.
In particular, it uses Rust 2018 and enables Github Actions.

CHANGELOG.md

@@ -4,7 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
-## Next
+## [Unreleased]
+
+### 2.8.0-beta.1 - 2023-09-09
 
 * **BIG:** Updated to Rust 2018
   * NOTE: Old 2015 crates will still work because of [excellent 2015/2018 compatibility](https://blog.rust-lang.org/2018/07/27/what-is-rust-2018.html#managing-compatibility)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "slog"
-version = "2.7.0"
+version = "2.8.0-beta.1"
 authors = ["Dawid Ciężarkiewicz <dpc@dpc.pw>"]
 description = "Structured, extensible, composable logging for Rust"
 keywords = ["log", "logging", "structured", "hierarchical"]