Improve ensure-package macro

- Rename to “ensure-library”, since I’m really trying to make sure a
  certain library is installed and calling something like the following
  is just silly:

    (ensure-package geiser-impl :package geiser)

- Rename the “:from” keyword parameter to “:package” since it is
  ambiguous when a “:path” keyword parameter is added, which could also
  be considered to determine from where a library is loaded.

- Add the “:path” keyword parameter, some libraries aren’t managed by
  package.el but by me. This parameter adds its value to the load path
  before attempting to check if it has been installed.

- Instead of checking if the package is installed and can be located,
  just try requiring it. This is easier for libraries not managed by
  package.el, since they will technically not be installed.

emacs/.emacs.d/init.el

@@ -50,24 +50,40 @@
 
 ;; This macro is inspired by use-package, but I want to maintain some
 ;; control of the syntax I use to configure my settings.
-(defmacro ensure-package (package &rest args)
-  "Make sure PACKAGE is installed.
+(defmacro ensure-library (library &rest args)
+  "Make sure LIBRARY is installed.
 
 ARGS should be a plist which may contain one of the following options:
 
-- :from
+- :package
 
   Specify which package should actually be installed to ensure
-  the library named in PACKAGE exists."
+  the library named in LIBRARY exists.
+
+- :path
+
+  Specify a path to add to the load path to be able to load this
+  package."
+  (declare (indent 1))
   (let ((library-symbol (cl-gensym))
-        (package-symbol (cl-gensym)))
-    `(eval-when-compile
-       (let ((,library-symbol ',package)
-             (,package-symbol ',(or (plist-get args :from) package)))
-         (unless (and (package-installed-p ,package-symbol)
-                      (locate-library (symbol-name ,library-symbol)))
-           (package-install ,package-symbol))
-         (require ,library-symbol)))))
+        (package-symbol (cl-gensym))
+        (path-symbol (cl-gensym))
+        (package (or (plist-get args :package) library))
+        (path (plist-get args :path)))
+    `(progn
+       (eval-and-compile
+         (let ((,path-symbol ,path))
+           (if ,path-symbol
+               (add-to-list 'load-path
+                            (if (file-name-absolute-p ,path-symbol)
+                                ,path-symbol
+                              (concat user-emacs-directory ,path-symbol))))))
+       (eval-when-compile
+         (let ((,library-symbol ',library)
+               (,package-symbol ',package))
+           (unless (require ,library-symbol nil :noerror)
+             (package-install ,package-symbol)
+             (require ,library-symbol)))))))
 
 ;;;; Helper functions: