Fixes #1945.

Now it's more like TrackballControls. This wheel zoom was too intensive finger action for me ;)

As per discussion in #1889.

Using xhr.addEventListener instead of xhr.onreadystatechange. Changed 'complete' event to 'load' as native JavaScript.

Also added rudimentary position-based vertex colors to MarchingCubes object and example for testing.

There is no normalization or anything, it's up to application layer not to set colors beyond <0,1> range.

This addresses issue #1834

As per suggestion in https://github.com/alteredq/three.js/commit/5d5f92d6411f3d39725ea704594d7a09ecb92cca

Only these 4 are actually valid for regular textures:

http://www.khronos.org/opengles/sdk/docs/man/xhtml/glTexImage2D.xml

We had it wrong before, it just accidentally worked as default type GL_UNSIGNED_BYTE is common for both data types and pixel types.

Also added optional quick-and-dirty UVs for MarchingCubes object, just to be able to test this. For the moment these are just XZ world coordinates.

This should address half of #1834

As per discussion in #855

To be tested if it works ...

See discussion here: https://github.com/alteredq/three.js/commit/2fd0b1b14deef40825d6a853ae0522f78d4b57d8

As per discussion in #1803.

It's really hard to tell if this has any affect at all as shader creation by itself is so costly it dwarfs everything else.

This seems to work.

This should address #1803

Todo:

- write some test
- hook this into material.needsUpdate handling
- figure out what to do with GL shader objects

Still need to fix influence sorting.

Maybe we need a build/custom/ThreeCore.js though...