Issue# 13313: Add Line Islands Standard Time

Okay. I updated the windows time zone name conversions per http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/zone_tzid.html and then added Line Islands Standard Time from http://support.microsoft.com/kb/2981580 (it has yet to be added to the first link).

In addition to that I put the script that I used to regenerate the time zone name conversions at the bottom of std.datetime so that it will be easier to make such updates in the future.

I also changed `tzDatabaseNameToWindowsTZName` and `windowsTZNameToTZDatabaseName` so that they return `null` on failure rather than throwing as explained here:

https://issues.dlang.org/show_bug.cgi?id=13319
I'm just using the list at http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/zone_tzid.html - specifically http://unicode.org/cldr/data/common/supplemental/windowsZones.xml. AFAIK, this is as close as it gets to having an official list of what the conversions are between the Windows time zones and those in the TZ Database.

To be honest, I think that if you really want the time zones to be correct, you should never use `WindowsTimeZone`. Rather, you should just provide the TZ Database files yourself and use `PosixTimeZone`. The Windows time zone info is rife with mistakes. But using it will make it so that you match what Windows users in those time zones will see (at least in theory), and it doesn't require providing the TZ Database files, so it makes sense to have `WindowsTimeZone` even if it's probably better not to use it in most cases.

As for Mexice specifically, it does have a separate list of time zones in the list, but there are quite a few TZ Database time zones which are treated the same under Windows, and there's nothing that we can do about that except maybe complain to MS about how much they suck at dealing with time zones and DST.