[tz] Several minor patches

Attached are another round of patches, relative to 62060419e3b81752ee5c1bda546c0ff87d66ea3e. 0001 expands a bit commentary in tz-art.htm. 0002 adjusts some Rule lines, since zic has been able to handle 24:00. This changes timestamps for one minute in Asia/Dhaka at the end of 2009-12-31 to better match the contemporaneous commentary. The rest are minor, with 0003 fixing up spacing in the UNTIL fields of Zone and Zone continuation lines, and with 0004 and 0005 fixing up commentary for consistency. These can be compared at https://github.com/timparenti/tz-experimental/compare/eggert:master...timpar... -- Tim Parenti