Exiftool support

[perk11]

I'd really like to see exiftool support in this module. Now I'm running it separately with -all= parameter and it is able to strip EXIF from some files even after all the recompressions.

Thank you for consideration.

[1000ch]

Meta data is already being reduced by other tools that grunt-image includes. Should it be supported in addition?

[perk11]

Last time I tried, I was able to stripped more metadata with exiftool even after using all other tools.

[1000ch]

That's nice. But exiftool is not standalone, so grunt-image require you to install exiftool with Homebrew or any instruction of other platform if supported...