Logging
*******

Functions to aid library logging. The default logging "Runlevel" is
usually NOTICE and above.

**Stem users are more than welcome to listen for stem events, but
these functions are not being vended to our users. They may change in
the future, use them at your own risk.**

**Module Overview:**

   get_logger - provides the stem's Logger instance
   logging_level - converts a runlevel to its logging number
   escape - escapes special characters in a message in preparation for logging

   log - logs a message at the given runlevel
   log_once - logs a message, deduplicating if it has already been logged
   trace - logs a message at the TRACE runlevel
   debug - logs a message at the DEBUG runlevel
   info - logs a message at the INFO runlevel
   notice - logs a message at the NOTICE runlevel
   warn - logs a message at the WARN runlevel
   error - logs a message at the ERROR runlevel

   LogBuffer - Buffers logged events so they can be iterated over.
     |- is_empty - checks if there's events in our buffer
     +- __iter__ - iterates over and removes the buffered events

   log_to_stdout - reports further logged events to stdout

stem.util.log.Runlevel(enum)

   Enumeration for logging runlevels.

   +------------+--------------------------------------------------------------+
   | Runlevel   | Description                                                  |
   |============|==============================================================|
   | **ERROR**  | critical issue occurred, the user needs to be notified       |
   +------------+--------------------------------------------------------------+
   | **WARN**   | non-critical issue occurred that the user should be aware of |
   +------------+--------------------------------------------------------------+
   | **NOTICE** | information that is helpful to the user                      |
   +------------+--------------------------------------------------------------+
   | **INFO**   | high level library activity                                  |
   +------------+--------------------------------------------------------------+
   | **DEBUG**  | low level library activity                                   |
   +------------+--------------------------------------------------------------+
   | **TRACE**  | request/reply logging                                        |
   +------------+--------------------------------------------------------------+
