Move away from serialize

[omus]

As pointed out by @tkelman we shouldn't be using Julia's serialize for long term storage. Since the serialize function shouldn't change for patch releases normally we should be ok but this could be an issue when working with Julia nightlies where the serialization implementation could suddenly change.

[melonedo]

What are the alternatives to serialize? Serializing the results to JSON/BSON would be portable, but less performant I think.

[omus]

What are the alternatives to serialize?

The main alternative I'm considering is using a variation of the tzfile format. TimeZones.jl already supports the official tzfile format so we could do some preliminary benchmarking.

[omus]

We've switched to using a serialization format similar to the tzfile format but with a couple of additional features. This format is the tzjfile format which was made specifically for TimeZones.jl in #380 and adopted as the default in #385