EpochConv

Epoch Converter

`EpochConv` for a buffer to convert between epoch and datetime

Default keybindings in the buffer
  + g0: reset all using *datetime or now*
  + g1: convert epoch to datetime
  + g2: convert datetime to epoch
  + g3: assign epoch to datetime
  + g4: assign datetime to epoch
  + g5: set epoch to now

See also:
  + https://github.com/bartek/epochconverter.nvim
  + https://github.com/hlucco/nvim-eswpoch
  + https://superuser.com/questions/590133