Separate NMEASentence values collection

[ptoews]

Started to resolve #107.
Separated the value collection into two methods, one for named values (by fields) returning a dict and another one without names returning just a list. Also integrated them into __repr__.
Here is how they work currently:

msg = pynmea2.parse("$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D")
msg.field_values()
Out[9]: 
{'timestamp': datetime.time(18, 43, 53, 70000),
 'lat': '1929.045',
 'lat_dir': 'S',
 'lon': '02410.506',
 'lon_dir': 'E',
 'gps_qual': 1,
 'num_sats': '04',
 'horizontal_dil': '2.6',
 'altitude': 100.0,
 'altitude_units': 'M',
 'geo_sep': '-33.9',
 'geo_sep_units': 'M',
 'age_gps_data': '',
 'ref_station_id': '0000'}
msg.unnamed_values()
Out[10]: []
repr(msg)
Out[11]: "<GGA(timestamp=datetime.time(18, 43, 53, 70000), lat='1929.045', lat_dir='S', lon='02410.506', lon_dir='E', gps_qual=1, num_sats='04', horizontal_dil='2.6', altitude=100.0, altitude_units='M', geo_sep='-33.9', geo_sep_units='M', age_gps_data='', ref_station_id='0000')>"

Some points to consider:

• Cast known/named values to their actual types e.g. float? This would be a separate issue/PR where probably the parsing of messages would have to be considered.
• Unit tests

[coveralls]

Coverage decreased (-1.0%) to 97.106% when pulling 69d1a9c on ptoews:fields_extraction into 4527cf4 on Knio:master.

[xOneca]

Could have been used keys() and values() (and items()?), like dicts do.

[xOneca]

My comment was on named_values() only. Also consider collections.namedtuple's _asdict().

[ptoews]

Are you referring to the names of the new methods? I agree there might be better alternatives.
But it's not that simple: There are fixed fields per Sentence class, which are named in fields, but there might also be additional values in data without any name. So a single items() or asdict() would be misleading, since not all the values are named and therefore are not suitable for a dict, and otherwise not all information would be included in the extracted data container.

[xOneca]

Just give them a name like _extra (or something like that) and let it be the extra data as a list, or add each one as _extra1, etc. Or fieldN.

[ptoews]

Thanks for your suggestion, I think this is indeed a better solution.

[ptoews]

Unit tests are now done as well. Anything else to do?

[howroyd]

Unit tests are now done as well. Anything else to do?

Awesome work.

Would be good for the readme to show an example.

[ptoews]

Done, let me know if there is anything else