changelog: prepare for 1.3 release

Author: BurntSushi

CHANGELOG.md

@@ -1,12 +1,23 @@
-UNRELEASED
-==========
+1.3.0 (2019-09-02)
+==================
+This release adds a plethora of new crate features that permit users of regex
+to shrink its size considerably, in exchange for giving up either functionality
+(such as Unicode support) or runtime performance. When all such features are
+disabled, the dependency tree for `regex` shrinks to exactly 1 crate
+(`regex-syntax`). More information about the new crate features can be
+[found in the docs](https://docs.rs/regex/*/#crate-features).
+
+Note that while this is a new minor version release, the minimum supported
+Rust version for this crate remains at `1.28.0`.
 
 New features:
 
 * [FEATURE #474](https://github.com/rust-lang/regex/issues/474):
   The `use_std` feature has been deprecated in favor of the `std` feature.
   The `use_std` feature will be removed in regex 2. Until then, `use_std` will
   remain as an alias for the `std` feature.
+* [FEATURE #583](https://github.com/rust-lang/regex/issues/583):
+  Add a substantial number of crate features shrinking `regex`.
 
 
 1.2.1 (2019-08-03)