Fixed Python unicode support.

Fixes issue #25

Allows Unicode support.

For example:
    
    import pyteaser
    pyteaser.Summarize(u'Título', u'Artículo. Contenido.')

Results in:
    
    [u' Contenido.', u'Art\xedculo.']

Instead of:
    
    Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "C:\Users\LVELEZ\Anaconda\lib\site-packages\pyteaser.py", line 86, in Summarize
    sentences = split_sentences(text)
    File "C:\Users\LVELEZ\Anaconda\lib\site-packages\pyteaser.py", line 215, in split_sentences
    s_iter = [''.join(map(str,y)).lstrip() for y in s_iter]
    UnicodeEncodeError: 'ascii' codec can't encode character u'\xed' in position 3:
    ordinal not in range(128)
    >>> pyteaser.Summarize(u'Título', u'Artículo. Contenido.')
    Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "C:\Users\LVELEZ\Anaconda\lib\site-packages\pyteaser.py", line 86, in Summarize
    sentences = split_sentences(text)
    File "C:\Users\LVELEZ\Anaconda\lib\site-packages\pyteaser.py", line 215, in split_sentences
    s_iter = [''.join(map(str,y)).lstrip() for y in s_iter]
    UnicodeEncodeError: 'ascii' codec can't encode character u'\xed' in position 3:ordinal not in range(128)