Generate energy figures.

This is a work in progress. This patch adds support for generating an
energy.json file with measurement for each benchmark.

[
  {
    "name": "/tmp/adpcm.x0",
    "results": {
      "energy": 0.000677114975708,
      "time": 0.0502976190476,
      "avg_power": 0.0134621675644,
      "avg_current": 0.00402593842456,
      "avg_voltage": 3.34386106232
    }
  }, {}
]

	* .gitignore: Add *.json.
	* energytool.py: New script. It probes for the energy measurement and
	ouputs JSON.
	* dejagnu/baseboards/atmega328p-shrimp.exp: Remove the energytool
	variable. We are using the energytool.py script instead.
	* dejagnu/baseboards/atxmega256a3bu.exp: Likewise.
	* dejagnu/config/avrdude.exp: Likewise.
	* dejagnu/config/energytool.exp: Likewise. Also output JSON for each
	measurement.
	* dejagnu/baseboards/avr-avrdude.exp: Match all the ouput of
	energytool.py.
	* gcc.beebs/execute.exp: Create and finalize the JSON energy data
	gathered.
	* run-avr.sh: Remote --energytool and add --energy-data for specifying
	a custom JSON energy data file.