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)*

proc-macros/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "graphite-proc-macros"
+version = "0.1.0"
+authors = ["Graphite Authors <contact@graphite.design>"]
+edition = "2018"
+publish = false
+
+[lib]
+path = "src/lib.rs"
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0.26"
+syn = { version = "1.0.68", features = ["full"] }
+quote = "1.0.9"
+
+[dev-dependencies.editor]
+path = "../editor"
+package = "graphite-editor"