Massive documentation update; fixes many issues. ...

Issues fixed by these documentation updates:

- #1973, fixed filter and BitmapText property docs
- #1908, fixed type reference links
- #1856, fixed name of MeshShader

fix a merge error from merging #1990

* Improved performance of adding and removing particles to ParticleContainer

Merge pull request #1833 from JiDW/tilingspritetrim ...

Fix tilingsprite from a spritesheet

Merge pull request #1925 from mreinstein/dev ...

update stale DisplayContainer docs. Remove broken normal filter.

Fix issues with multiple ParticleContainers; #1989 ...

This rebases the commits in #1989 to squash them into a single commit and
to remove the extra merge commits in @bchevalier's repo.

Add callback for when children change; #1988 ...

This is a rebase of the commits in #1988 to squash it down to a single
commit and remove the extra merge commits in @bchevalier's repo.

add batchSize param to ParticleContainer; #1990 ...

This is a rebase of the commits in #1990 to squash to a single commit and
remove the extra merge commits in @bchevalier's repo.

fixed canvas renderer options bug; added roundPixels to default render options

fix iterator for VideoBaseTexture.fromUrls so that it finds the source and mime by index

Merge pull request #1944 from tiriana/feature/sprite-dimensions-for-negative-scale ...

Ensure that sprite width and height are never negative

changed sgn to sign

add missing drawCount increments

CavasRendered.roundPixels can now be set from options

ensure that sprite width and height are never negative

update docs to reflect sprite support in v3 #1639

quick particle container destroy fix

graphics renderer tidy up.. ...

removed a few evil console logs..

missed a semicolon..

fixes #1850 ...

bit of a funny one.. when at the canvas is resized we now set the scale
mode again as it seems to be reset

tweaked graphics ...

Should be faster with static graphics content now (which is what its
designed for!)

Merge pull request #1836 from drkibitz/chore/cleanup ...

Chore/cleanup

Depecrate `PIXI.math` namespace ...

Access math members from PIXI when outside of core, require the math module directly when inside of core.

fix typos

uuid is a misnomer, this is not universal, but it is unique in the scope of pixi ...

Added deprecation for uuid

Remove the rest of internal module coupling between packages

Remove internal filter aliases on PIXI.filters, expose on PIXI instead as PIXI.AbstractFilter ...

These are undocumented and unecessarily create a tight coupling between core and filters where the filters package is actually responsible for exposing an internal core module.

Cleanup, remove references to old files PolyK SpineRuntime

send Container as reference on added/removed events. #1870

trigger 'added' and 'removed' events for Container children.