Add pep8 config, use pep8 in travis

also, fix E111-E113 errors:
E111 - indentation is not a multiple of four
E112 - expected an indented block
E113 - unexpected indentation

On Mon, Dec 29, 2014 at 07:45:48AM -0800, Joachim Durchholz wrote:
>    In [1]setup.cfg:
> 
>  > @@ -0,0 +1,12 @@
>  > +[pep8]
>  > +# E101 - indentation contains mixed spaces and tabs
>  > +# W191 - indentation contains tabs
>  > +# W291 - trailing whitespace
>  > +# W293 - blank line contains whitespace
>  > +# E111 - indentation is not a multiple of four
>  > +# E112 - expected an indented block
>  > +# E113 - unexpected indentation
> 
>    That doesn't say we can't use the previous stable version.
>    It just says we can't use 1.5.7.
> 
>    I'm proposing to use 1.5.6, and stick with it until we decide that some
>    future revision of pep8.py fits our needs better.

Can you explain why?

It has same issue, that fixed only in the git version:
$ ../../pep8/pep8.py 
./sympy/core/add.py:110:25: E113 unexpected indentation
./sympy/core/add.py:113:25: E113 unexpected indentation
./sympy/core/mul.py:211:29: E113 unexpected indentation
./sympy/core/mul.py:214:29: E113 unexpected indentation
./sympy/core/mul.py:217:29: E113 unexpected indentation
./sympy/core/mul.py:222:29: E113 unexpected indentation
./sympy/core/mul.py:420:29: E113 unexpected indentation
^C... stopped