Memory optimization

• Unload Text assets after using them.
• Added option to cache Geo database for quicker access if time zones change often, at the cost of more memory usage.

Initial Release

• Initial release, based on https://github.com/mattjohnsonpint/GeoTimeZone/ but adapted to work in Unity WebGL.
• Because WebGL has no access to TimeZoneInfo.FindSystemTimeZoneById(String) a custom implementation had to be built to calculate the offsets from UTC. The information was gotten from https://github.com/rxaviers/iana-tz-data/blob/master/iana-tz-data.json. This is IANA time zone data converted to json for easier parsing. In the future this should be preferably gotten from IANA directly