DynDNS: simple shell script to update DNS entry with a current IP address

The aim of the script is to automate changing of an IP address in the DNS
config. Script reads current IP address and if it has changed, updates
bind configuration file and uploads it via ssh to a remote server and runs
update command.

All zones to be updated shall be located in subdirectories. Each
subdirectory shall contain .config file with env variables to be defined.

Variables to be configured in .config in each directory:
  TMPL: name of the file with the template (local)
  OUTFILE: name of the resulting zone file (local)

  SSH_PARAMS, SCP_PARAMS: parameters to be passed to ssh/scp

  SSH_SRV: name of the remote server

  DESTFILE: name od the target zone file (remote)

  SSH_CMD: script to be executed to refresh data (remote)

Template file should use two variables: %SERIAL% and %IP%.