Restructure project directories (#333)

`/client/web` -> `/frontend`
`/client/cli` -> *delete for now*
`/client/native` -> *delete for now*
`/core/editor` -> `/editor`
`/core/document` -> `/graphene`
`/core/renderer` -> `/charcoal`
`/core/proc-macro` -> `/proc-macros` *(now plural)*

editor/src/misc/mod.rs

@@ -0,0 +1,8 @@
+#[macro_use]
+pub mod macros;
+pub mod derivable_custom_traits;
+mod error;
+pub mod test_utils;
+
+pub use error::EditorError;
+pub use macros::*;