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
Not a blocker or anything, but I'm just trying to understand the logic behind this change. So why is it that we're merging multiple timezones into some seemingly arbitrarily-chosen standard name? Is this the official standard name used by Windows so we need to do the same in order to be conformant? I'm concerned about some timezones that are equivalent only some of the time but not all (e.g., within the last few years I remember a change in North American daylight savings time, such that the dates for which daylight savings apply are now different from the dates Mexico uses; as a result, even though a US timezone may be otherwise identical to a corresponding Mexican timezone, merging them into one will cause the wrong set of daylights saving dates to be applied). I'm assuming this situation doesn't apply to this code here, am I right?