Switch to tdoc for importing/exporting Markdown (#8)

* richtext: Remove ElementId, as block ids are not necessary anymore.

* Add tdoc bridge, get rid of our own Markdown import

* Update tdoc version

* Update tdoc

* Fix clippy issues

Author: roblillack

Cargo.lock

@@ -10,6 +10,7 @@ repository.workspace = true
 piki-core = { version = "0.2.0", path = "../core" }
 fltk = { version = "1.5.20", features = ["use-wayland"] }
 pulldown-cmark = "0.13.0"
+tdoc = { version = "0.8.0" }
 clap = { version = "4.5", features = ["derive"] }
 walkdir = "2.5"
 regex = "1.10"