Read a reST file into a string.

def read_file(self, infile):
        """Read a reST file into a string.
        """
        try:
            with open(infile, 'rt') as file:
                return file.read()
        except UnicodeDecodeError as e:
            err_exit('Error reading %s: %s' % (infile, e))
        except (IOError, OSError) as e:
            err_exit('Error reading %s: %s' % (infile, e.strerror or e))