Feature : Global ignore list (Issue #79)

Ignore list is read from an environment variable named
PIDCAT_IGNORED_TAGS. Multiple tags can be set, separated
by a semicolon.

eg: on *nix systems just type the following in a terminal
$ export PIDCAT_IGNORED_TAGS="art;dalvikvm"

pidcat.py

@@ -24,6 +24,7 @@
 import argparse
 import sys
 import re
+import os
 import subprocess
 from subprocess import PIPE
 
@@ -128,6 +129,8 @@ def indent_wrap(message):
   'DEBUG': YELLOW,
 }
 
+ENV_IGNORED_TAGS = os.getenv('PIDCAT_IGNORED_TAGS',"").split(';')
+
 def allocate_color(tag):
   # this will allocate a unique format for the given tag
   # since we dont have very many colors, we always keep track of the LRU
@@ -330,7 +333,9 @@ def tag_in_tags_regex(tag, tags):
     continue
   if args.tag and not tag_in_tags_regex(tag, args.tag):
     continue
-
+  if tag_in_tags_regex(tag, ENV_IGNORED_TAGS):
+    continue
+
   linebuf = ''
 
   if args.tag_width > 0: