Update README

Author: jacob-hughes

README.md

@@ -5,28 +5,14 @@ libgc is a garbage collector for Rust. It works by providing a garbage-collected
 
 # Structure
 
-There are three repositories which make up the gc infrastructure:
-    - **libgc** the main library which provides the `Gc<T>` smart pointer and its
+There are two repositories which make up the gc infrastructure:
+
+* **libgc** the main library which provides the `Gc<T>` smart pointer and its
       API.
-    - **libgc_internal** contains the gc allocation and collector logic. This is
-      collector specific, and can be conditionally compiled to support different
-      implementations. At the moment, it only supports a single collector
-      implementation: the Boehm-Demers-Weiser GC. Users should never interact
-      directly with this crate. Instead, any relevant APIs are re-exported
-      through libgc.
-    - **rustgc** a fork of rustc with GC-aware optimisations. This can be used to
+* **rustgc** a fork of rustc with GC-aware optimisations. This can be used to
       compile user programs which use `libgc`, giving them better GC
       performance. Use of rustgc is not mandated, but it enables further
       optimisations for programs which use `libgc`.
 
 This seperation between libgc and rustgc exists so that a stripped-down form of
-garbage collection can be used without compiler support. The further split
-between libgc and libgc_core exists to make linkage easier when the rustgc
-compiler is used.
-
-rustgc needs access to the GC's `Allocator` implementation. This exists in the
-libgc_internal crate so that it can be linked to the target binary either as
-part of libgc, or as part of the rust standard library (if compiled with
-rustgc). libgc contains code which would not compile if it was packaged as part
-of rustgc. To prevent duplication, the libgc_interal crate will link correctly
-as either a standard cargo crate, or as part of the rust core library.
+garbage collection can be used without compiler support.