Reorganize unit-tests and test workflow

+ Moved unit tests out of tests/ and into their respective modules.
+ Rewrite makefile and added these tasks:
  + <MODULE>/<SUBMODULE> -- byte-compile a specific module
  + test:<MODULE>/<SUBMODULE> -- runs tests for a specific module
  + testi -- run tests in an interactive session of Emacs (WIP)
  + run -- opens an Emacs session with this config; useful when it is in
    a non-standard location.

core/autoload/test.el

@@ -1,10 +1,15 @@
 ;;; core/autoload/test.el -*- lexical-binding: t; -*-
 
 ;;;###autoload
-(defmacro def-test-group! (name &rest body)
-  (declare (indent defun))
+(defmacro def-test! (name &rest body)
+  "Define a namespaced ERT test."
+  (declare (indent defun) (doc-string 2))
   (unless (plist-get body :disabled)
-    (dolist (form body)
-      (when (eq (car form) 'ert-deftest)
-        (setf (cadr form) (intern (format "test-%s-%s" name (symbol-name (cadr form)))))))
-    `(progn ,@body)))
+    `(ert-deftest
+         ,(cl-loop with path = (file-relative-name (file-name-sans-extension load-file-name)
+                                                   doom-emacs-dir)
+                   for (rep . with) in '(("/test/" . "/") ("/" . ":"))
+                   do (setq path (replace-regexp-in-string rep with path t t))
+                   finally return (intern (format "%s::%s" path name))) ()
+       ()
+       ,@body)))