The opacity attribute for an object was encoded as rgba (only if the
opacity was not 0 or 1). This worked OK if the SVG document was rendered
in a browser, but not when rendered using Inkscape or Illustrator. In
those programs a transparent object would be rendered as black since the
rgba attribute is not recognized.Using fill-opacity, like in previous
versions of SVGRenderer, makes the transparent objects render as
expected.

It does not used if line contains the only segment

Such method can be used directly at the end of rendering loop

While SVG is text format, 10-digits for each coordinate is overkill. In
many cases on can use precion=1 or even precision=0. For instance,
instead of 
path
d="M95.67875432291896,61.48774395485388L99.22967055503229,-179.38931463976644"

one gets (with precision 1)

path d="M95.7,61.5L99.2,-179.4"

This significantly (factor 2) reduces size of SVG when stored into the
file. 

Avoid explicit usage of fill-opacity or stroke-opacity
One could provide similar function in THREE.Color object itself

When SVG stored into the file, reduces file size by ~5%

If several svg:path with same style should be created, just concatenate
there 'd' attributes and make single svg:path node. Will highly reduce
size of SVG if many elements with similar color should be rendered.

Now rendering of all elements done with svg:path

Replace it by svg:rect

Idea to use svg:path for all SVG primitives.
Later one can concatenate svg:path if they have identical styles

This reverts commit 632002cb.

Conflicts:
	src/Three.js

Fixes #5570