add support for mentalab devices

[Andrey1994]

Signed-off-by: Andrey Parfenov a1994ndrey@gmail.com

Tested on windows, can connect to device and get data.

Todo and issues:

• can connect to device only when LED is blue and blinking, after some time it gets green and you have to restart the device
• temperature data looks completely wrong, its a random value between 20 and 120, need to check parsing
• accel and gyro data, instead expected values like -1..0..1(these units used in brainflow) I get something I dont understand, the same in explorepy, so its not an issue with parsing
• add docs about explore 4 and 8 channels boards
• add release notes to website
• need to test on linux and macos, have no hardware
• cannot test correctness of eeg parsing(I dont get how to connect these electrodes), dont understand the idea of 5th channel... is it a reference which should be subtracted from other channels? these value does not change for me
• it seems like fw supports timestamp syncronization, need to implement it or at least use sampling rate to correct timestamps which come from batches of datapoints
• need to test 8 chan board, have no device

To do later in case of requests:

• add support for sending commands(at least for sampling rate and maybe on\off)
• add support for impedance measurement

[Andrey1994]

data_env.csv
data_orn.csv
data_eeg.csv

data files from explore.py example attached, still dont understand values there

[Andrey1994]

Update:

its not a parsing issue in brainflow for accelerometer, using explorepy I get the same values:

accelerometer
[ -19.093 -134.627 1011.746]

[Andrey1994]

temperature is also correct, I looked at the wrong column before

[Andrey1994]

fixed linux issue, fixed parsing, added commands for sampling rate and test signal. validated against explorepy using test signal