doc: improve & complete documentation on many sensors

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

TODO

@@ -0,0 +1,27 @@
+Easy:
+MAX7221 - SPI 8 digit LED
+- https://mbed.org/components/MAX7221/
+- 
+SCA61T - inclinometer SPI
+- https://mbed.org/components/SCA61T-Inclinometer/
+DS1721 - i2c temperature/thermostat
+- https://mbed.org/components/DS1721/
+MPL3115A2 - i2c altimeter
+- https://mbed.org/components/MPL3115A2/
+- http://www.ebay.co.uk/itm/Barometric-Pressure-Altitude-Temperature-Sensor-I2C-MPL3115A2-/221499210102?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item339261b976
+TEMT6200 - Ambient light sensor
+- https://mbed.org/components/TEMT6200/
+CMPS03 - i2c digital compass
+- https://mbed.org/components/CMPS03-Digital-Compass/
+- http://www.ebay.co.uk/itm/Magnetic-Compass-CMPS03-/221437925374?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item338eba97fe
+- http://www.robot-italy.com/it/cmps03-robot-compass-module.html
+
+Medium
+E-ink sharp 1.3" LCD
+- https://mbed.org/components/13-SHARP-Memory-LCD/
+LCD-S401
+- https://mbed.org/components/Lumex-LCD-S401/
+
+Hard:
+RA8875 - 480x272 SPI 4 wire
+- https://mbed.org/components/RA8875-Based-Display/