Initial inet data type implementation

[mkgrgis]

Based on storage conventions, discussed on SQLite forum thread.
Default affinity of IPv4 - integer. Default affinity of IPv6 - blob, because other compact forms are impossible.
Storage convention for blob affinity:

 m - mask as number of bits
a - bytes of IP address
IP v4 + cidr
┏━━━┳━━━┳━━━┳━━━┳━━━┓
┃ a ┃ a ┃ a ┃ a ┃ m ┃
┗━━━┻━━━┻━━━┻━━━┻━━━┛
0 1 2 3 4 - byte index
IP v6 + cidr
┏━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┓
┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ m ┃
┗━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┛
0 1 2 3 4 5 5 7 8 9 10 11 12 13 14 15 16 17 - byte index
IP v4
┏━━━┳━━━┳━━━┳━━━┓
┃ a ┃ a ┃ a ┃ a ┃
┗━━━┻━━━┻━━━┻━━━┛
0 1 2 3 - byte index
IP v6
┏━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┳━━━┓
┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃ a ┃
┗━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┻━━━┛
0 1 2 3 4 5 5 7 8 9 10 11 12 13 14 15 16 - byte index

[mkgrgis]

@t-hiroshige , please assign a reviewer for this PR. This not easy and not hard PR mainly similar to some previous PR about MAC addresses support.