ENH: closing issues #395, #449, #570, #571
Fix column string formatting; index and header options to to_string; decorator for docstrings; floating point prettier printing. Also added to release notes & documentation. Address #395, #449, #570, #571

This is great. You have some trailing whitespace problems-- is your editor configured to strip trailing whitespace? I think we can set git to do it automatically on commit. 

The new string formatting looks awesome. There's a tiny buglet with padding zeros on scientific notation:

```

            A          B          C          D        
2000-01-03 -1.656e-08 -7.652e-08  9.046e-08  1.231e-07
2000-01-04  2.767e-08 -3.075e-08  1.148e-08  1.398e-08
2000-01-05 -1.505e-07 -6.278e-08  1.732e-08 -9.14e-080
2000-01-06 -7.624e-09 -4.579e-08  9.167e-08  2.895e-08
2000-01-07  1.238e-07  2.228e-07  6.408e-08 -2.168e-07
2000-01-10 -9.959e-08 -7.705e-09  6.522e-08  8.063e-08
2000-01-11  1.75e-070  8.02e-080  4.244e-08 -8.221e-08
2000-01-12  1.178e-08  1.204e-09  1.877e-07  2.385e-07
2000-01-13  7.682e-08  1.259e-07  1.135e-07 -1.111e-07
2000-01-14  4.326e-09  1.043e-08 -8.295e-08  6.293e-08
2000-01-17 -2.4e-0700 -1.156e-07  1.866e-08  1.331e-07
2000-01-18  8.905e-08 -1.822e-07  6.108e-08 -1.147e-07
2000-01-19 -1.088e-07  2.057e-08  1.323e-07 -1.07e-070
2000-01-20 -4.258e-08 -5.991e-08 -1.944e-07 -8.385e-08
2000-01-21  1.297e-07  9.573e-08  4.32e-080  7.103e-09
2000-01-24 -1.045e-07  5.521e-08  4.563e-08 -1.843e-08
2000-01-25 -1.461e-07 -7.573e-09  1.283e-07  1.451e-07
2000-01-26 -1.063e-07 -1.561e-07  1.223e-07  1.332e-07
2000-01-27  9.289e-08  9.192e-08  6.909e-08  5.926e-08
2000-01-28  5.496e-08  5.334e-08 -3.28e-070 -1.086e-07
2000-01-31 -7.841e-08  3.568e-08  3.921e-08 -1.512e-07
2000-02-01 -1.123e-07  6.324e-08  1.773e-07 -3.672e-08
2000-02-02 -1.42e-070 -1.12e-070  1.044e-07 -2.402e-09
2000-02-03  7.559e-08  8.136e-08  2.631e-08  1.09e-070
2000-02-04 -2.969e-08  4.038e-08  1.433e-07  2.184e-09
2000-02-07  1.106e-07 -4.719e-08  8.871e-08 -7.917e-08
2000-02-08 -7.816e-08 -3.934e-08 -8.182e-08 -1.172e-07
2000-02-09  1.354e-07 -1.268e-07 -5.352e-08  1.918e-08
2000-02-10 -1.104e-07 -2.125e-07 -2.127e-07  3.835e-08
2000-02-11  6.909e-08  1.969e-07 -1.518e-07 -7.226e-09
```

Can fix it separately after merging this-- the rebase was somewhat terrifying but appears to have gone through cleanly
 OK I think I got that buglet licked here:

https://github.com/wesm/pandas/commit/94fbd7853756812c3cdcfe9637e0f1463bfb8dce

and off to bed :) 
