tools (common/async_process): remove useless encoding + use full path for command: - arguments don't need to be encoded anymore, `spawnProcess` handles str directly now - use full path even for first argument: even if first argument should be only executable name, it appears that using full path only in `command` is not enough (seen with Python where system installation is used instead of the VirtualEnv one when full path is not used as first argument). (grafted from 25cbaf04772855cd8aead18771465a4f00f5fa03)

You'll find install instructions in documentation (see doc/installation.rst).

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