Fixes #4: Update to use Certbot. Rename from letsencrypt to certbot.

tasks/main.yml

@@ -1,7 +1,7 @@
 ---
-- name: Clone Let's Encrypt into configured directory.
+- name: Clone Certbot into configured directory.
   git:
-    repo: "{{ letsencrypt_repo }}"
-    dest: "{{ letsencrypt_dir }}"
-    version: "{{ letsencrypt_version }}"
-    update: "{{ letsencrypt_keep_updated }}"
+    repo: "{{ certbot_repo }}"
+    dest: "{{ certbot_dir }}"
+    version: "{{ certbot_version }}"
+    update: "{{ certbot_keep_updated }}"