Make clock use local time zone

[psvenk]

Currently, the time zone to be used in the clock is hard-coded as UTC-5 (or UTC-4 when Daylight Savings Time is observed). Not only does this exclude users who are not in the Eastern US or Canada, but it also inconveniences maintainers because the hard-coded time zone needs to be switched whenever Daylight Savings Time begins or ends. I suggest using the user's local time zone instead; possibly this can be configured using an option after #23 is implemented.