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

Am 28.12.2014 um 00:37 schrieb Sergey B Kirpichev:
> On Sat, Dec 27, 2014 at 02:13:31PM -0800, Joachim Durchholz wrote:
>>   > +# E113 - unexpected indentation
>>
>>     "Unexpected indentation" can happen for an indented comment, which is not
>>     a syntax error.
>
> In that case - no error or warning will be raised.

What can I say - I'm seeing these warnings.

Here's the pep8 output from my Eclipse installation:

Description: E113 unexpected indentation
Severity: Warning
On element: test_risch.py
In folder: sympy-project/sympy/sympy/integrals/tests
Location: line 237

This is the code:

     assert integrate_hyperexponential(a, d, DE) == \
         (exp(2*tan(x))*tan(x) + exp(tan(x)), 1 + t1**2, True)
         # exp(2*tan(x))*tan(x) + tan(x) + exp(tan(x))