Update ChangeLog and bump version for v2.6.0-rc1

Bump ABI: 5.3.2 -> 5.4.0

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

ChangeLog.md

@@ -8,7 +8,16 @@ All notable changes to the project are documented in this file.
 --------------------
 
 ### Changes
+- New APIs from the [Infix Project](https://github.com/kernelkit/infix):
+  - `fexistf()`
+  - `vfopenf()`
+  - `popenf()`
+  - `vreadsnf()`, `readsnf()`, `writesf()`
+  - `vreadllf()`, `readllf()`, `readdf()`
+  - `writellf()`, `writedf()`
+
 ### Fixes
+- Spellchecking of API docs
 
 
 [v2.5.3][] - 2023-04-08