Tell ipython directive to ignore deprecation warnings from numpy

Apparently currently np.linalg.lstsq gives a warning if you don't pass
rcond explicitly, and the ipython directive errors out if you get an
unexpected warning. I don't care about any of this, so shut it up.

Author: njsmith

doc/library-developers.rst

@@ -120,6 +120,7 @@ And here's how it can be used:
        exec(f.read())
 
 .. ipython:: python
+   :okwarning:
 
    from patsy import demo_data
    data = demo_data("x", "y", "a")

doc/quickstart.rst

@@ -43,6 +43,7 @@ method attached, so we can pass them directly to a regression function
 like :func:`np.linalg.lstsq`:
 
 .. ipython:: python
+   :okwarning:
 
    outcome, predictors = dmatrices("y ~ x1 + x2", data)
    betas = np.linalg.lstsq(predictors, outcome)[0].ravel()