Convert time between different time zones.

`tzc-convert-time` to convert a given time from one time-zone to another
`tzc-convert-time-to-favourite-time-zones` to convert a given time from one
time-zone to a list of favourite time-zones.

A list of favourite time zones could be set using like following
(setq tzc-favourite-time-zones-alist '(("Asia/Kolkata" "Kolkata") ("America/New_York" "New York") ("Europe/Berlin" "Berlin")))