Kill node.js addon, use Emscripten based simulator instead

Tests are passing, however those that require verifying I/O are
currently disabled. Need to add to the protocol functions for setting
fake I/O and getting notified on changes.
Update serialport dependency
Travis: Don't symlink clang executables

Seems to not be needed anymore, and caused failures
Revert "Makefile: Use own avrdude implementation for flashing"

Does not seem to work just yet
This reverts commit d55a75ff94013da4b7e1ded97d2051ab04f6a670.