JSON output for basic tools

I have merged into libsmartcols support for JSON format. The feature is currently enabled for lsblk(8), findmnt(8), lslocks(8) and losetup(8). The library already uses structured data, so add a different output format is pretty trivial. For example findmnt(8) and lsblk(8) are able to gather much information and standardized parsable format makes it easy to use it monitoring tools, automatic bug reporting tools, etc.

$ lsblk --json -o name,type,mountpoint                                    
{                                                                         
   "blockdevices": [                                                      
      {"name": "sda", "type": "disk", "mountpoint": null,                 
         "children": [                                                    
            {"name": "sda1", "type": "part", "mountpoint": "/boot/efi"},  
            {"name": "sda2", "type": "part", "mountpoint": "/boot"},      
            {"name": "sda3", "type": "part", "mountpoint": "/home"},      
            {"name": "sda4", "type": "part", "mountpoint": "/"},          
            {"name": "sda5", "type": "part", "mountpoint": "/home/wine"}, 
            {"name": "sda6", "type": "part", "mountpoint": "[SWAP]"}      
         ]                                                                
      },                                                                  
      {"name": "sdb", "type": "disk", "mountpoint": null,                 
         "children": [                                                    
            {"name": "sdb1", "type": "part", "mountpoint": "/home/archive"}
         ]                                                                
      }                                                                   
   ]                                                                      
}                                                                         

                                                                    
$ findmnt --json --submounts /home                                        
{                                                                         
   "filesystems": [                                                       
      {"target": "/home", "source": "/dev/sda3", "fstype": "ext4", "options": "rw,relatime,data=ordered",
         "children": [                                                    
            {"target": "/home/wine", "source": "/dev/sda5", "fstype": "ext4", "options": "rw,relatime,data=ordered"},
            {"target": "/home/archive", "source": "/dev/sdb1", "fstype": "ext4", "options": "rw,relatime,data=ordered"}
         ]                                                                
      }                                                                   
   ]                                                                      
}

For the next Monday my TODO contains "JSON sfdisk/libfdisk dump output"...