Parse advertising interval as float
Parse advertising interval as float

Parse `env.BLENO_ADVERTISING_INTERVAL` as a float, allowing users to better control the min/max advertisement interval sent in the `LE_SET_ADVERTISING_PARAMETERS_CMD` HCI packet. The `math.floor` call will still ensure that values sent in the HCI packet are ints.

For some reason I don't understand, Apple [recommends several specific advertising intervals](https://developer.apple.com/library/content/qa/qa1931/_index.html). Most of these intervals are floats, which become nice round ints after being multiplied by 1.6.
sandeepmistry/bleno