Merge branch 'patch-1' into develop (PR #156)

Merge branch 'patch-1' into develop (PR #156)

This merge updates the build_hdate code so that years < 1000 result in zero-
padded four digit years in date strings. Without the changes in this merge,
ungrib.exe was unable to extract data from, e.g., files with fields valid in
the year 450, failing due to

hdate 450-01-01_00:00:00 > hsave 0000-00-00_00:00:00

not evaluating as true in one of the internal loops. This was apparently
caused by a formatting error when hdate was created.

The solution adopted in this merge is to change the 'i4' format to 'i4.4' on
lines 26, 30, 34 and 38 in build_hdate.F. The previously failing comparison now
works as

hdate 0450-01-01_00:00:00 > hsave 0000-00-00_00:00:00

.

Thanks to Ozan Mert Göktürk (@ozanmert) for contributing this fix.

* patch-1:
  Update build_hdate.F