Add imports to lib init file

powerline/ext/tmux/segments.py

@@ -2,7 +2,7 @@
 
 import os
 
-from powerline.lib.memoize import memoize
+from powerline.lib import memoize
 
 # Weather condition code descriptions available at http://developer.yahoo.com/weather/#codes
 weather_conditions_codes = {

powerline/ext/vim/segments.py

@@ -4,7 +4,7 @@ import os
 import vim
 
 from powerline.ext.vim.bindings import vim_get_func
-from powerline.lib.memoize import memoize
+from powerline.lib import memoize
 from powerline.lib.vcs import guess
 
 vim_funcs = {

powerline/lib/__init__.py

@@ -0,0 +1,2 @@
+from humanize_bytes import humanize_bytes
+from memoize import memoize