Prepare changelog for 6.4.0.

CHANGELOG.md

@@ -2,6 +2,22 @@
 
 ## Unreleased
 
+### Notes
+
+### Added
+
+### Removed
+
+### Changed
+
+### Fixed
+
+### Deprecated
+
+### Contributors
+
+## [6.4.0](https://github.com/ISibboI/evalexpr/compare/6.3.0...6.4.0) - 2021-07-21
+
 ### Notes
 
  * Minimum supported Rust version (MSRV) increased to `1.46.0`
@@ -11,8 +27,6 @@
 
  * Allow scientific notation in float literals
 
-### Removed
-
 ### Changed
  
  * Made some functions `const`. This increased the MSRV
@@ -21,8 +35,6 @@
 
  * `eval_number` methods returned `EvalexprError::ExpectedFloat` before, now they correctly return `EvalexprError::ExpectedNumber`
 
-### Deprecated
-
 ### Contributors
 
 My warmhearted thanks goes to