An installed version of esptool.py may be required

To cope with the constant change of the bundled esptool in esp8266/Arduino
makeEspArduino now require an installed version for some of the flashing
operations. If missing an error message will be shown.

One more Python variable needed

Change needed for Python3 path

Triggered by syntax change in Arduino config files

OTA improvements and fix for esp32 board names

Fix `ota` when password is empty. (plerup#113)

* Fix `ota` when password is empty.

* Let `espota.py` use its own defaults.

Added support for ccache and user defined make rules

Show flash info also in latest version of Arduino

Some modifications for latest esptool handling

Main output file names are now configurable

Fixed missing tabs in previous PR

One more change needed for new lwip format

Avoid double slashes in file paths for Mac