Refactor Makefile to compile as package.el does

Order sources alphabetically to reflect the order in which package.el
compiles package files, and remove all file dependencies, as package.el
doesn't care for byte compilation deps anyway.

Also compile all files in a single Emacs instance, to preserve side
effects.
Merge all EPL code back into a single file

We now always use an explicit `epl-package` structure, which has a
internal field for the underlying package descriptor.  All EPL
operations now determine at runtime, how to access the descriptor.

This makes things a lot easier to handle, and avoids all sorts of fuckup
from the byte compiler (such as expanding macros defined in file A,
though file A is never loaded a runtime).
Fix the commentary
Don't use environment variables in Makefile

Fixes compilation from within Emacs, as Emacs exports `$EMACS=t` in
compile-mode, which is pretty stupid and breaks `cask exec $(EMACS)`.
Add required cl-lib dependency

Required for Emacs 24.2 and earlier.
Suppress spurious byte compiler warnings
Remove legacy package.el

We do not load it anymore.  Clients of this library are now responsible
for making package.el available.
Merge pull request #6 from cask/fix-byte-compiler-fuckup

Fix byte compiler fuckup