doc(book): remove implemented ideas

Remove the sections from the ideas sections that have already been
implemented recently.

book/src/ideas.md

@@ -2,12 +2,6 @@
 
 The following are general ideas for this project, that are not yet implemented or even close to being developed, but definitely on the list of ideas for the future.
 
-## Documentation generator
-
-Similar to Rust's [rustdoc](https://doc.rust-lang.org/rustdoc/index.html), it would be nice to have a documentation generator built in. The doc comments can be extended to be parsed as Markdown and allow for rich formatting in the docs.
-
-As a nice side effect, if parsing the comments as Markdown upfront it can be used to transform the docs into native documentation where Markdown is not supported (for example JavaDoc in Java/Kotlin projects).
-
 ## Central registry for schemas
 
 Rust has [crates.io](https://crates.io) as central repository for sharing libraries. In similar fashion, a registry for schema files could be created. It would allow easy sharing of schemas.
@@ -21,11 +15,3 @@ Something that is missing from crates.io is to allow for private registries that
 The schema allows for certain changes that are backwards compatible and do not create a break in the wire format. That means older generated code is still able to read the data despite being created by a newer version of the schema. But the rules are difficult to always keep in mind and mistakes can easily be made.
 
 To avoid accidental breaking changes, it would be nice to have an auto-detection mechanism that compares the current version to a previous one whenever changes are made. The _old_ version could be the current Git HEAD compared to the local changes.
-
-## Schema evolution
-
-When decoding a value, it may contain new fields and enum variants that are not known to the decoder yet. This can happen if the schema changed and but was only updated in one of two parties. For example a server might have introduced new fields to a response, but not all clients have updated to the new schema yet.
-
-The same can happen the other way around. For example, if the data was saved in some form of storage and the schema evolved in the meantime, the decoder might encounter old data that lacks the newer content.
-
-In both cases, the schema must be able to handle missing or unknown fields. Several rules must be upheld when updating a schema, to ensure it is both forward and backward compatible.