Migrate to UglifyJS v3 and use its comment preservation feature

[natevw]

At least as of the current Uglify3, it has builtin support for comments preservation. This migrates to that version.

This may have been requested via a mysterious "issue #7" mentioned in a few others, which GH won't let me access for some reason. This should also fix a number of other open issues (probably #19 and #20; not sure about #21).

Note that a few of the default uglify options had to change since they were moved around and/or no longer available. I preserved the ones that I could, and updated the tests to not worry so much about the specific defaults.

[natevw]

@davglass Do you think you'll have a chance to review and possibly publish this on npm soon? I'm running into an issue where django-pipeline is intermittently giving us bad JS builds due to the current yuglify comment handling, and need to deploy some resolution to that in the next couple days if possible.

[natevw]

With uglify-js@3.1.4, we ended up running into some issues with hoist_vars: true (which I set based on the original lift_vars: true of older versions). The UglifyJS documentation discourages using it, so I wonder if it just hasn't been tested much.

Anyway, this project seems thoroughly dead so instead of updating this patch, I've opted to just reconfigure django-pipeline to use Uglify and CSS Min directly:

PIPELINE = {
# old
#    'YUGLIFY_BINARY': os.path.join(HG_ROOT, 'node_modules/.bin', 'yuglify'),

# new
    'JS_COMPRESSOR': 'pipeline.compressors.uglifyjs.UglifyJSCompressor',
    'UGLIFYJS_BINARY': os.path.join(HG_ROOT, 'node_modules/.bin', 'uglifyjs'),
    'UGLIFYJS_ARGUMENTS': '--mangle --compress --comments /^!/',
    'CSS_COMPRESSOR': 'pipeline.compressors.cssmin.CSSMinCompressor',
    'CSSMIN_BINARY': os.path.join(HG_ROOT, 'node_modules/.bin', 'cssmin'),

    # …other config…
}

Likewise replacing "yuglify": "github:natevw/yuglify#uglify3-comments" in package.json with "cssmin": "^0.4.3", "uglify-js": "^3.1.5".