Improved array handling: Fixes for issue npm/ini#52 and should also fix npm/ini#56

[sthuber90]

For instance handling systemd-networkd .network files is now working for duplicate keys. An example is provided below.

For a eth0.network file:

[Match]
Name=eth0

[Network]
Address=172.16.1.99/24
Gateway=172.16.1.1
DNS=172.16.1.1
DNS=8.8.8.8

The file is now parsed to:

{
  "Match": {
    "Name": "eth0"
  },
  "Network": {
    "Address": "172.16.1.99/24",
    "Gateway": "172.16.1.1",
    "DNS": [
      "172.16.1.1",
      "8.8.8.8"
    ]
  }
}

And encoded to the following string when using the new option isArray (Ideas for better naming are welcome):
ini.stringify(parsed, { isArray: false})
"[Match]\nName=eth0\n\n[Network]\nAddress=172.16.1.99/24\nGateway=172.16.1.1\nDNS=172.16.1.1\nDNS=8.8.8.8\n"

otherwise if you prefer to have [] present as a suffix after the key in a .ini file and it does not corrupt what the file is used for you can do as follows:
ini.stringify(parsed, { isArray: true})
or
ini.stringify(parsed)
will return:
"[Match]\nName=eth0\n\n[Match.Network]\nAddress=172.16.1.99/24\nGateway=172.16.1.1\nDNS[]=172.16.1.1\nDNS[]=8.8.8.8\n"

[wraithgar]

#204 solves this problem w/ a flag