[x3d-public] new feature in X3dTidy stylesheet: numeric significant-digits precision using regular expression (regex)

[Michalis Kamburelis]

Note that I'm aware that our tools (Castle Model Converter, Castle Model Viewer etc.) are ones to blame here. I do plan to fix this (generate floats with less significant digits, by default) on our side.

We will by default output 6 digits after dot, not more (6 matches defaults I observed in various applications, including game engines like Unity when they same scene files).

So give me time, this will be fixed on our side too :)

Just to give some context why it took / takes me so long to address this:

- Some X3D authors really rely on preserving small numbers -- yes, differences smaller than 0.001 sometimes matter.

- Numbers in X3D (and 3D in general) undergo scaling (e.g. by Transform.scale), so some people use tiny numbers are rely that later e.g. scaling mesh by 100 makes a reasonable result.
- People sometimes design tiny tiny worlds.
- the UNIT clause (introduced in X3D 4 from what I recall) also means that we don't always have meters. We _typically_ have meters, I agree with that statement in Don's mail, but it's not just always the case.
- Sometimes, people put tiny difference to make sure one thing is on top of another, to avoid visual Z-fighting. E.g. plane at Z = 0.0001 will be on top of plane with Z = 0.0, even if visually the distance between them will seem ~practically nothing.

- That's the reason why I was reluctant to just arbitrarily cut any possibly-useful digits (even if possibility that they are useful, and not noise coming from rounding to decimals, was very small :) ) by default. I needed to first have a way to _precisely_ store 32-bit floats to files, to give a solution to people who will need it.

- We now have it, as we started work on "save to glTF", with binary data representing floats, and thus we can save 32-bit floats from memory -> files without any loss of precision and in compact way.
- This means that for text output formats, like X3D XML / classic, we are fine cutting digits. If anyone will need arbitrary precision, we can just recommend saving to glTF which will preserve the in-memory 32-bit float perfectly, since the "binary float" is just a direct dump of memory 32-bit float, no text conversion, no rounding.

Stay tuned for announcements when I finish all I talk above :)

Regards.
Michalis
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