Update python coding style
Update python coding style

Since Beagleterm is base on hterm of chromium.
BeagleTerm's python style also mainly follow Chromium style guide https://chromium.googlesource.com/chromium/src/+/master/styleguide/styleguide.md#Python
RandomlyKnighted/beagle-term,RandomlyKnighted/beagle-term,beagleterm/beagle-term,beagleterm/beagle-term