ENH: Change truncation ellispsis to unicode character
Changes the truncation symbol from '...' to the math characters horizontal, vertical and diagnol ellipsis as proposed in https://github.com/pydata/pandas/pull/7086#issuecomment-42862717. 

In the Ipython Notebook, the result looks like this

http://nbviewer.ipython.org/gist/bjonen/492fea9559fd73edf579

To do: 
- Do we need to fall back to simple strings in certain environments (https://github.com/pydata/pandas/pull/7086#issuecomment-42999103)? 
