Fix compiling

[kalwalt]

This pull request wants to fix the code that fails during the building process and try to improve it a little bit. it is related to this issue https://github.com/artoolkitx/jsartoolkit5/issues/78 In the specific;

• The building process fails while try to build the libar.bc because including the file Video/VideoLuma.c
• i added an env var to link emscripten in the package.json file
• minor things (cleaning the code)

I have tested only on a linux machine, i have no idea for other OS (Windows, Mac..) , I used to build the lib the latest emscripten 1.38.26. Let me know if you think that the code should be merged or not.

[kalwalt]

I receive this error running the simple_video.html example ( and the others using the debug lib):

artoolkit.api.js:1148 Uncaught TypeError: artoolkit.setup is not a function
    at ARController._initialize (artoolkit.api.js:1148)
    at ARController.<anonymous> (artoolkit.api.js:111)
    at ARCameraParam.<anonymous> (artoolkit.api.js:1591)
    at writeCallback (artoolkit.api.js:1785)
    at writeByteArrayToFS (artoolkit.api.js:1811)
    at XMLHttpRequest.oReq.onload (artoolkit.api.js:1828) 

i saw this issue https://github.com/artoolkitx/jsartoolkit5/issues/40 but it seems that now the debug lib is affected and not the minifyied lib...

[kalwalt]

this PR is outdated, will be closed. Follow this new https://github.com/artoolkitx/jsartoolkit5/pull/86