Add scan subnet functionality

[AlexJuca]

This feature contains the following changes:

1. Adds the capability to scan a given subnet
2. Updates README.md and added a section describing how to perform a subnet scan.

iex> Hades.new_command()
...> |> Hades.add_argument(Hades.Arguments.ScanTechniques.arg_sP())
...> |> Hades.add_target("192.168.120.42/24")
...> |> Hades.scan()
02:28:50.664 [info]  NMAP Output: "Starting Nmap 7.80 ( https://nmap.org ) at 2020-03-02 02:28 W. Central Africa Standard Time\r\n"

02:29:09.001 [info]  NMAP Output: "Nmap scan report for 192.168.100.1\r\n"

02:29:09.001 [info]  NMAP Output: "Host is up (0.00s latency).\r\nMAC Address: F8:75:88:9D:F9:B5 (Huawei Technologies)\r\n"

02:29:09.001 [info]  NMAP Output: "Nmap scan report for 192.168.100.2\r\n"

02:29:09.001 [info]  NMAP Output: "Host is up (0.047s latency).\r\nMAC Address: 78:31:C1:D0:87:8E (Apple)\r\n"

02:29:24.300 [info]  NMAP Output: "Nmap scan report for 192.168.100.3\r\n"

02:29:24.300 [info]  NMAP Output: "Host is up.\r\n"

02:29:26.568 [info]  NMAP Output: "Nmap done: 256 IP addresses (3 hosts up) scanned in 36.03 seconds\r\n"

02:29:26.584 [info]  Port exit: :exit_status: 0


02:29:26.584 [info]  DOWN message from port: #Port<0.83>
%{
  hosts: [
    %{hostname: "", ip: "192.168.100.1F8:75:88:9D:F9:B5", ports: []},
    %{hostname: "", ip: "192.168.100.278:31:C1:D0:87:8E", ports: []},
    %{hostname: "", ip: "192.168.100.3", ports: []}
  ],
  time: %{
    elapsed: 36.03,
    endstr: "Mon Mar 02 02:29:26 2020",
    unix: 1583112566
}

[AlexJuca]

@fklement I chose to use the same add_target/1 function to do the subnet scan. It would be intuitive for most nmap users to just add the "/24", "16" subnet at the end eg (add_target("192.168.100.1/24") instead of having add_target(ip, "/24").

[fklement]

Overall a good implementation. Would be nice if you address my comments.
Since I also want to increase the test coverage of this library, it would be nice if you could write some tests for different use cases.

[fklement]

I'm not quite sure why you first split the target and then stitch it back together without any checking.
It would be nice if you could include some test here to see if the subnet mask one specified is valid.

[fklement]

I think the code would look cleaner if you continue to use the old "structure" nmap #{option} -oX #{path}....
Just use the target variable to compose the given #{target} / #{subnet} or #{target}.

Another option that just came in my mind would be to build the target string in the hades.ex module so you don't have to handle this here. I think this would reduce the overall loc a bit.

[AlexJuca]

I agree on making the code cleaner. Will work on this.

[matteing]

Hey, any merge timeline on this?

[AlexJuca]

Hey, any merge timeline on this?

I have not had the time to work on the suggestions requested by @fklement but my fork does have a working implementation.