Correctly compute ultra-zoomed line paths [fixes #217]

[etpinard]

@alexcjohnson @mdtusz

Issue #217 is two months old now and after numerous attempts at fixing it the right way by adding more complexity to the already-complex line decimation algorithm, I gave up.

This PR removes the clip-multiple constrain in the linear to pixel convert routine. This has three effects:

1. Ultra-zoomed line paths (where 4 segment pts are beyond the clip-multiple constrain) are now computed correctly, fixing Line paths are not correctly computed when their points are well-beyond the axis ranges #217.
2. Far-off-edge points now have coordinates of very large magnitude that some browser's svg renderers may not understand. Note: I couldn't find any documentation on the svg limits.
3. The line decimation algorithm is slowed down as now far-off-edge points are not de facto clusters anymore.

I decided to make this PR because I thought that fixing #217 was more important than side-effects 2. and 3. above. I hope you agree.

[etpinard]

this mock looks like:

on master.

[mdtusz]

I did some researching on this before as well and came to the same conclusions (unless we were to implement a much more complex truncate-at-the-plot-borders line decimation method). I couldn't find anything on maximal svg values either - I would think that svg rendering can accomodate arbitrarily large numbers and interpolate what to render if a coordinate lies outside those bounds.

In any case, if we do encounter issues with this, it will be easy enough to revert to the old solution, or create a more robust one instead.

💃

[alexcjohnson]

Sure. Actually it seems like the way getTolerance is implemented, the points will continue to get sparser and sparser as they get farther away, so it's likely this won't have too much effect on performance anyway. 💃

[alexcjohnson]

At some point it may be worthwhile to look into making getTolerance more aggressive (superlinear in distance from the viewport, perhaps, at least to a point) but this will need some heavy testing to make sure it doesn't introduce new failure modes.