Configuration format rework

[elkowar]

This is the massive PR you've all been waiting for!

We're replacing XML as the configuration language with a custom, s-expression based configuration syntax named yuck.

yuck puts a lot of focus on providing clean, readable and useful error messages where possible, and aims to at some point allow for the implementation of advanced development-tooling such as a language server. To achieve that, eww is now split up into several crates:

• yuck: the main configuration syntax parser, API to deal with parsed ASTs and the datastructures that represent a basic interpreted eww configuration file.
• simplexpr: (weird name, I don't care) The parser and evaluator for the inline infix expressions eww allows for. These where previously possible to use in {} within string literals. This crate provides not only the AST structure and evaluation logic, but also the dynval value, which is a string-value that may be interpreted as a value of other types depending on where it is used. DynVal is thus the main primitive value type used for typejuggling, and replaces PrimVal from the old eww codebase.
• eww_shared_util: a small crate that provides types and functions used across some of the other crates. Mainly, it provides the Span type used throughout the codebase.
• eww: The core eww codebase. This contains all of the server-logic, GTK related code, as well as anything else not directly related to the configuration file.

This PR is still work in progress for several reasons:

• Error handling could still take a good bit of improvement. Not only do I still see multiple places where better diagnostics could be provided, but also I still see some issues with how the code is structured right now. As this is not a "breaking" change in any way, I might merge this PR before all of those error-handling related tasks are fully done - I don't want to block the syntax migration longer than necessary just to pursue some form of "PR-purity" or whatever.
• The documentation needs to be adjusted - this is not yet done at all. @manderio has agreed to help me out here
• The examples need to be migrated to the new syntax
• A release / tag before the rework should be made, so people that don't want to migrate right away don't have to search through hundrets of commits to find the version prior to the rework
• I want to find an alternative syntax for string literals that doesn't conflict with " in shell-scripts - this shouldn't be hard, I just don't know what syntax to choose yet

However - this is a cursive statement - but:
It should be usable. There might still be dealbreaking bugs, I haven't tested everything - if there are, please leave a comment here.
If you want to be the early adopter, feel free to give this a try! The syntax is (most likely, I'll not rule it out 100%, but it's very unlikely) not gonna go through any big changes - if any at all, those will be minor changes of keywords or some additions to syntax. So if your stuff that you do now works, it'll most likely continue working once this is fully finished!

Have fun!

PS: Note that this PR may get some force pushes still, as I do want to clean up the commit history - so maybe don't build big branches on top of this right now

Other changes

During work on this PR, some other changes have been made during refactorings.

• add --logs flag
• start daemon when other commands (i.e. eww open) don't find a daemon
• Apply the changes made in Initial X Window configuration cleanup #217

Notes / TODOs

• Allow comments in simplexprs
• Include shell error message in script-execution failures, and mention "Failed to execute script" in the error message explicitly

[undefinedDarkness]

A pr of 116 commits...
Truly astounding

[elkowar]

note: checks failing because of rust-lang/rust#88043 - nightly moment

[VuiMuich]

Awesome! 🎉
Congrats on this milestone achievment! 🥳