Add pep8 config, use pep8 in travis
PEP 8 fixes:

 E101 - mix of tabs and spaces
 W191 - use of tabs
 W291 - trailing whitespace
 W293 - trailing whitespace
 E111 - 4 spaces per indentation level
 E112 - 4 spaces per indentation level
 E113 - 4 spaces per indentation level
 W292 - no newline at end of file
 W391 - blank line at end of file

see http://pep8.readthedocs.org/
Merge pull request #300 from skirpichev/pep8-1

Use pep8 in travis builds