ssh: add programs.ssh module

This module generates a `.ssh/config` file. This doesn't embed _all_
options for the ssh client, but the most common ones should be there.

Example usage:

```nix
  programs.ssh = {
    enable = true;
    forwardAgent = true;
    controlMaster = "auto";
    matchBlocks = [
      {
        host = "something.blah.edu";
        port = 1024;
        user = "cleague";
        identitiesOnly = true;
      }
      {
        host = "host1 host2 host2.net host2.com";
        port = 7422;
        hostname = "example.com";
        serverAliveInterval = 60;
      }
      {
        host = "lucian";
        forwardX11 = true;
        forwardX11Trusted = true;
        checkHostIP = false;
      };
    };
  };
```

Each entry in `programs.ssh.matchBlocks` must contain a `host` field,
which will be used for the block condition.

1 files changed, 1 insertions, 0 deletions

diff --git a/modules/default.nix b/modules/default.nix
index ebec6c96fb5..e1f6b652686 100644
--- a/modules/default.nix
+++ b/modules/default.nix
@@ -20,6 +20,7 @@ let
     ./programs/git.nix
     ./programs/gnome-terminal.nix
     ./programs/lesspipe.nix
+    ./programs/ssh.nix
     ./programs/texlive.nix
     ./services/dunst.nix
     ./services/gnome-keyring.nix