Changes since v0.5:

Bugfixes:
- bugfix: 'geoip-shell on' command errors out on iptables-based systems
- bugfix: when changing the update cron schedule, old cron job does not get removed
- bugfix: in some edge cases, the update cron job may not be created
- bugfix: incorrect mask bits used when creating a rule allowing ipv6 link-local connections (/8 instead of /10)
- bugfix: geoip-shell-fetch.sh: fix running without root permissions

Improvements:
- nftables variant: attach the base chain to the prerouting netfilter hook with priority -141 (rather than -150) to make rules processing deterministic when other rules exist which have priority 'mangle' (-150), making it easier to create custom rules which will be processed before geoip-shell rules
- include information on currently used firewall backend utility (nftables or iptables) in the status report
- avoid unnecessary re-fetching of ip lists when running 'geoip-shell configure'
- randomize the default update schedule's minute between 10 and 20 (previously was always 15)
- randomize the automatic update second between 0 and 59
- improve console messages and the status report
- update and improve the general documentation
- improve OpenWrt-specific documentation

Signed-off-by: Anton Khazan <antonk.d3v@gmail.com>