Provide a machine readable way to determine the available generators and other capabilities of the binary

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

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As per this thread providing some easily parsed way of determining the available generators for IDEs would be useful. For example, cmake -E capabilities might produce:

 {
   "generators": [
     {
       "name": "Unix Makefiles",
       "multiconfig": false,
       "recursive": true,
       "extraGenerators": ["Sublime", "CodeBlocks"]
     },
     {
       "name": "Ninja",
       "multiconfig": false,
       "recursive": false,
       "extraGenerators": ["Sublime", "CodeBlocks"]
     },
     {
       "name": "Xcode"
       "multiconfig": true,
       ...
     }
     ...
  ],
  "daemon": {
    "protocolVersions": ["3.5", "3.6"]
  }
 }