Garminconnect

* Added Chinese signin URL to prevent login issues by sydongda

* Added new body battery API call get_body_battery() by dpfrakes
* Fixed bug in garmin.get_hrv_data() returning wrong format by psdupvi

* Added daily step data summary endpoint for date range by dpfrakes
* Fixed spelling errors fixed by cclauss
* Small cleanups

* Added API call and example to fetch activity exercise sets
* Added API call and example to fetch progress summary
* Fix unset method. Garmin requires it now to be a DELETE request
* Fix for device alarm api call when value is 'null', also added example to fetch them
* Fix in example.py for fetching activities
* Added API calls and example to get gear data, e.g. shoes etc
* Experimental HRV api call added

A big thank you to all contributors for their input, bug reports and PR's!

* Added get_goals method to API client (status param can be "active", "future", or "past"
* Added all 3 variations to example program
* Fix typos in README.md and example.py
* Removed json from pip install instruction (json is a built-in lib)
* Renamed variable copied from activities API methods
* Fixed AttributeError regarding 'download_activities' in example.py

* Replaced upload_fit_activity() with upload_activity() which supports more filetypes