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.