ValueError when importing unicode_literals from __future__

[Hugo]

Windows 7, Python 2.7.11, Astral 1.1

This code works (from the example code at https://pythonhosted.org/astral/#example ):

```
#!/usr/bin/env python
# encoding: utf-8
from __future__ import print_function
# from __future__ import unicode_literals
import datetime
from astral import Astral # pip install astral

city_name = 'London'
a = Astral()
a.solar_depression = 'civil'
city = a[city_name]

print('Information for %s/%s\n' % (city_name, city.region))

timezone = city.timezone
print('Timezone: %s' % timezone)

print(' Latitude: %.02f; Longitude: %.02f\n' % \
    (city.latitude, city.longitude))

sun = city.sun(date=datetime.date(2009, 4, 22), local=True)
print('Dawn: %s' % str(sun['dawn']))
print('Sunrise: %s' % str(sun['sunrise']))
print('Noon: %s' % str(sun['noon']))
print('Sunset: %s' % str(sun['sunset']))
print('Dusk: %s' % str(sun['dusk']))
```

Outputs:
```
M:\bin>python test.py
Information for London/England

Timezone: Europe/London
 Latitude: 51.50; Longitude: -0.12

Dawn: 2009-04-22 05:12:06+01:00
Sunrise: 2009-04-22 05:48:46+01:00
Noon: 2009-04-22 12:58:56+01:00
Sunset: 2009-04-22 20:09:00+01:00
Dusk: 2009-04-22 20:45:39+01:00

```

But uncommenting `from __future__ import unicode_literals` it gives:
```
M:\bin>python test.py
Traceback (most recent call last):
  File "test.py", line 10, in <module>
    a.solar_depression = 'civil'
  File "C:\Python27\lib\site-packages\astral.py", line 1493, in solar_depression
    self._depression = float(depression)
ValueError: could not convert string to float: civil
```

[Hugo (hugovk)]

One fix:

Change:
    def solar_depression(self, depression):
        if isinstance(depression, str):

to:
    def solar_depression(self, depression):
        if isinstance(depression, str) or isinstance(depression, unicode):

---

Another fix:

Add as first import:
from __future__ import unicode_literals

In latitude(self, latitude), longitude(self, longitude), solar_depression(self, depression):

Change:
        if isinstance(depression, str):

to:
        if isinstance(depression, unicode):

---

For both, there may be other similar changes to make elsewhere in the code; tests should find them.

[Hugo (hugovk)]

Please let me know when this has been released.

[Hugo (hugovk)]

Thanks, confirmed fixed with Astral 1.2.