Doc-Doctesting

Initial commit to test building on travis. Inculdes some initial fixes to the .rst files which were added while debugging the errors on my machine. 

Extension of issue #588 
As far as I can tell, py.test can't find the code in the .rst files without that extra argument. I think it might restrict us to .rst files insofar as docs are concerned (like if we wanted to use .txt for example. The default is .txt actually.)

http://pytest.org/latest/doctest.html explains that the default for this value is *.txt.

It does not appear to have any effect on docstrings in functions. From my tests:

    blaze/expr/table.py: [doctest] blaze.expr.table PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.Apply PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.By PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.Column PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.ColumnWise PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.Head PASSED
    blaze/expr/table.py: [doctest] blaze.expr.table.Join PASSED