htu21d: update to correct code now under MIT license

Signed-off-by: William Penner <william.penner@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
mpl3115a2: sensor added

Signed-off-by: William Penner <william.penner@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
gas: fixed documentation typos and updated images

Signed-off-by: Mihai Tudor Panu <mihai.t.panu@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
ldt0028: Added support for LDT0-028 PZT film-based sensors

Signed-off-by: Sarah Knepper <sarah.knepper@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>