FTP IANA source unreliable

[omus]

TimeZones.jl retrieves its information directly from IANA's FTP server. This server commonly cannot be connected to resulting in the error message from the download function:

curl: (56) Recv failure: Connection reset by peer

We currently are automatically retrying to download files up to three times which works most of the time but can still cause Travis builds to fail or be annoying for first time uses. We should either find some reliable mirrors or maybe keep a copy of the timezone rules within the repo.

[omus]

One other reason to find an alternative source is to avoid issues with firewalls. Some networks disallow the ports required for transferring data via FTP.