improved WeatherPoint class and updated ArchiveStruct B

[saveriogzz]

this is my attempt at replicating #5 's code and adapting it to python3. The _ArchiveBStruct and _TimeStruct are entirely taken from @bgkerion (kudos deserved!) .

Methods to get and set the console time, which makes use of _TimeStruct, have not yet been written

TODOs

• [x] method _fields_to_weather_point --> check how it will instantiate a WeatherPoint object
• [x] add option to report metric or imperial system of measurements --> marked done since it is a job for another PR

Some other fixes include minor PEP style improvements.

[saveriogzz]

hey @cmcginty , sorry I didn't ping you for the review! I left a few comments along the way, cheers!