pyotp.parse_uri does not convert 'interval' or 'counter' to int

OTP uri's that specify a period or initial count do not work since they are stored as str instead of int.
This makes e.g. totp.now() fail because totp.timecode() divides by self.interval which currently is a str when period is specified in the uri.

Simple fix in parse_uri line 87 and 89 cast to int:

elif key == 'period':
otp_data['interval'] = int(value)
elif key == 'counter':
otp_data['initial_count'] = int(value)