I think it is time to clean up our root folder
.travis.yml and requirements.txt added by @tkoyama010 seem to be irrelevant anymore, after Travis stopped serving open source projects for free
extract_gmm++ could be moved to the bin folder, what do you think @yves.renard ?
NEWS and ChangeLog are required by GNU standard but we do not really use them. So I suggest to remove, and silence any errors/warnings from autotools.
.codecov.yml does not seem to be used by @tkoyama010 anymore, can we remove it?