Generate individual icon crates and main library crate; Select icons through enum variants

[lpotthast]

Work in progrss. I found it much easier to get rid of the individual components at this point. Try it out if you like. What do you think? Can elaborate further if you like. Splitting into multiple crates would be required at this point I think...

[carloskiki]

This has potential, could this idea work well with #8?

I don't know the limitations of crates.io; Would shipping/updating 15 different crates be easily automatable?

[lpotthast]

Hey @Carlosted, I think that the PR is now in a state which can be merged. Feel free to check it out. The following things have changed:

• A manually implemented crate leptos-icons-core was added, containing a shared data structure for svg icon data.
• For each icon package, an individual crate is generated, named leptos-icons-* with * being the short name of the package, containing the parsed SVG data as conditionally compiled constants (using the shared data type to reduce wasm binary size).
• All these crates do not even need any leptos dependency anymore and could be used in more ways.
• Each crate also provides an enum with one variant for each icon (all conditionally compiled). The enum can map its variants to the respective icon data.
• The leptos-icons crate resolves the icon data from the given enum variant and manually generates a leptos svg element (brings more control over which attributes are actually set and with what data).
• The leptos-icons crate brings an additional enum, containing a variant for each icon-package enum. From implementations are generated to map from any leptos-icons-* enum to the leptos-icons enum variant containing that package-specific enum.

• That way, users can always specify icons like this:

  use leptos_icons::*;
  
  <LeptosIcon icon=BsIcon::BsFolder" />

  using a package-specific enum, even though the LeptosIcon component requires a value of its own enum. BsIcon is in scope, as leptos_icons reexports all package-specific crates. As soon as a user activates one icon using its feature, the enum from the corresponding icon-package will be in scope.