case insensitive bool parsing
From mailing list:

This is something that surprised me.
When reading from csv the values "True" and "False" are converted to bool, while "TRUE" and "FALSE"' to object
Using a converter {...: np.bool} I could take it into account.
Is it useful to take more possibilities into account knowing that there are a lot of possibilies True/False,  Yes/No,  ....?

In [19]: data = '''A;B
   ....: True;False
   ....: False;True'''
In [20]: df = pd.read_csv(StringIO(data), sep=';')
In [22]: df.dtypes
Out[22]: 
A    bool
B    bool

In [23]: data = '''A;B
   ....: TRUE;FALSE
   ....: FALSE;TRUE'''

In [24]: df = pd.read_csv(StringIO(data), sep=';')

In [25]: df.dtypes
Out[25]: 
A    object
B    object

In [27]: df = pd.read_csv(StringIO(data), sep=';', converters={'A':np.bool})

In [28]: df.dtypes
Out[28]: 
A      bool
B    object
