API that reports the reading from the htu21d sensor

Gets:

• /api/h

{
    "humidity": "49.3"
}

• /api/t

{
    "temperature": "23.8"
}

• /api/conditions

{
    "humidity": "49.0",
    "temperature": "23.8"
}

Dependencies

• express
• htu21d-i2c

Note: Does not build on 4.0.0 due to i2c lib support

TODO:

• remove unneeded jade/css/boilerplate code