Adafruit-circuitpython-bme280

* Removed use of `frozenset()`
* Refactor and tweaks to `pressure` property
* thanks barbudor for the updates

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](http://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.

Class attributes added to allow more control over the sensor. Thanks jraber.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](http://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](http://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](http://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](http://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.

Added dew point calculation using the Magnus forumla.

To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).

To use in CPython, `pip install adafruit-circuitpython-bme280`.

Read the [docs](https://circuitpython.readthedocs.io/projects/bme280/en/latest/) for info on how to use it.