[tz] Add new timezone for Hanoi Capital, Vietnam

[Paul Eggert]

On 2/18/19 10:07 AM, KP wrote:
> https://vi.m.wikipedia.org/wiki/Giờ_ở_Việt_Nam 
> <https://vi.m.wikipedia.org/wiki/Gi%E1%BB%9D_%E1%BB%9F_Vi%E1%BB%87t_Nam>

This cites the same source that we've used for our Vietnam data. If the 
web page contains other information that would be relevant to tzdb, 
please let us know.

The source is cited in the 'asia' file as follows:

# Trần Tiến Bình's authoritative book "Lịch Việt Nam: thế kỷ XX-XXI 
(1901-2100)"
# (Nhà xuất bản Văn Hoá - Thông Tin, Hanoi, 2005), pp 49-50,
# is quoted verbatim in:
# http://www.thoigian.com.vn/?mPage=P80D01
# is translated by Brian Inglis in:
# https://mm.icann.org/pipermail/tz/2014-October/021654.html
# and is the basis for the information below.

I checked a printed copy of Trần's book and verified that the 
thoigian.com.vn quote is verbatim.

WorldCat says there's another version of Trần's book dated 2013:

https://www.worldcat.org/oclc/946663040

However, WorldCat lists only two copies of this version in the world's 
libraries (one in the Library of Congress, the other in the Bibliothèque 
nationale de France). Also, there's a good chance that the WorldCat 
listing is in error, or that the 2013 edition's updates (if any) don't 
affect tzdb. So I haven't investigated this.