ENH: Changes the default offset for time_rules.market_open to 1, and
makes it an offset from 13:30 UTC.

This is to be more consistent with the market_close, which is an offset
from 20:00 UTC.

This also makes market_open and market_close cache the dt to offset from
for each day.
BUG: HistoryContainer creation at runtime did not work as intended.