multiboot2: update changelog, prepare v0.15

Author: phip1611

multiboot2/Changelog.md

@@ -1,5 +1,15 @@
 # CHANGELOG for crate `multiboot2`
 
+## 0.15.0 (2022-XX-XX)
+- `BootInformation` now publicly exports the `get_tag` function allowing you to work with custom
+  tags. An example is given in the documentation of the method (check docs.rs). There is also
+  a small unit test that you can use to learn from.
+- Additionally, this feature comes with the public type exports:
+  - `SpecifiedOrCustomTagTypeSerialized`
+  - `SpecifiedOrCustomTagType`
+- There exists a seamless integration between `u32`, `TagType`, `SpecifiedOrCustomTagType`, and
+  `SpecifiedOrCustomTagTypeSerialized` via `From` and `PartialEq`-implementations.
+
 ## 0.14.0 (2022-06-30)
 - **BREAKING CHANGES** \
   This version includes a few small breaking changes that brings more safety when parsing strings from the