Correct character for degrees symbol.

Don't know what the previous was encoded in, probably some Windows encoding.
Add object and methods for accessing DOP data in GNSS class.
Add methods to GNSSParam for changing update intervals of NMEA sentences

As described by Martin Furter on the NavSpark forum:
http://www.navspark.com.tw/blog/tutorial-using-uart1?commentId=6653778%3AComment%3A1892