Add markdown formatting to fedmsg err emails.

This way, we can copy and paste the emails directly into github/pagure issues to
track them.  Like this one, for instance:
https://github.com/fedora-infra/pdc-updater/issues/18

roles/fedmsg/base/templates/logging.py.j2

@@ -152,20 +152,24 @@ class ContextInjector(logging.Filter):
 hefty_format = """Message
 -------
 [%(asctime)s][%(name)10s %(levelname)7s]
+```python
 %(message)s
+```
 %(farewell)s
 
 Process Details
 ---------------
-host:     %(host)s
-PID:      %(pid)s
-name:     %(proc_name)s
-command:  %(command_line)s
-msg_id:   %(msg_id)s
+- host:     %(host)s
+- PID:      %(pid)s
+- name:     %(proc_name)s
+- command:  %(command_line)s
+- msg_id:   %(msg_id)s
 
 Callstack that lead to the logging statement
 --------------------------------------------
+```python
 %(callstack)s
+```
 """