add nodemcu-tool upload option

[matsievskiysv]

In light of #127 it would be useful to have two options for uploading files. This PR adds ability to use nodemcu-tool instead of nodemcu-uploader. This feature is controlled by make USE_NODEMCU_TOOL variable.

For example, following command will use nodemcu-uploader to upload file http/underconstruction.gif:

make upload FILE=http/underconstruction.gif PORT=/dev/ttyUSB0

This command will use nodemcu-tool:

make upload FILE=http/underconstruction.gif PORT=/dev/ttyUSB0 USE_NODEMCU_TOOL=1