Remove common.log (API break)

Small API break, replace:
 from byexample.common import log
 log(<msg>, <lvl>, <concerns>)
by
 from byexample.log import clog
 clog().<lvl-method>(<msg>)

clog() will search for the best logger based in which part of the
execution is and it will log through the concerns (event methods)
if they are available otherwise it will log to the terminal/console.

byexample/common.py

@@ -33,15 +33,6 @@ def build_where_msg(where, owner, msg=None, use_colors=False):
 
     return ''.join(tmp)
 
-
-def log(msg, lvl, concerns=None):
-    if isinstance(lvl, int):
-        if lvl >= 0:
-            print(msg)
-
-    else:
-        concerns.event('log', msg=msg, level=lvl)
-
 def colored(s, color, use_colors):
     if use_colors:
         if color == 'none':