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)*

frontend/assets/12px-solid/fullscreen-enter.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 12 12">
+	<polygon points="11,8 11,11 8,11 8,12 12,12 12,8" />
+	<polygon points="1,1 4,1 4,0 0,0 0,4 1,4" />
+	<polygon points="4,11 1,11 1,8 0,8 0,12 4,12" />
+	<polygon points="11,1 11,4 12,4 12,0 8,0 8,1" />
+</svg>