Copy the popup config instead of extending

Fixes #13.
Update settings comments, as mentioned in #13
Update the default prompt configurations
Use a separate keybindings for Linux and Windows

They are technically still the same, but we just defined all keybindings
twice for OSX which is definitely not desireable.
Add several config files to command palette
Move non-ST-reliant code in a subdirectory

Notably "format_date.py" and the pytz lib.
Close our ZipFile handle when plugin is disabled

It doesn't really help at anything because ST still keeps an open
handle, but whatever.
Remove microseconds from iso format

They hardly provide any value because the precision doesn't make sense
in this context. If you really need it, you can use ".%f".
Add "unix" to default configs
Make generate_table copy into the clipboard
Update README.md
Revise install.md

Also add a link to the available timezones to the settings.
Push version to 1.0.0
Finish v1.0.0