[Proposal] Split apart the standard library into multiple packages

[eliaslfox]

Currently Coalton's standard library is spread across 21 files. Many functions are prefixed to avoid name collisions. Users of Coalton must avoid top level definitions that collide with the standard library, and could ever collide with the standard library. To remedy this the following changes should be made to the package layout.

• macros in macros.lisp are moved to coalton.
• definitions in types.lisp and builtins.lisp are kept in coalton-library
• other files are moved to separate packages such as coalton-library/vector and have prefixes removed from their definitions. They intended to be imported with package local nicknames as vector and cell.
• A new package called coalton-prelude is created to reexport classes, list functions, and other currently un-prefixed definitions.
• coalton-user would :use coalton and coalton-prelude.