Renames concatenateToArray to appendToArray
Zero the height and width of the Cached canvases before deleting.

This reduces peak RSS by about 300 MiB on my Mac when scrolling slowly through
the first 30 pages of a scanned black and white document.
faster JPEG transform
Merge pull request #4955 from timvandermeij/rename-concatenate

Renames concatenateToArray to appendToArray
Merge pull request #4959 from nnethercote/zero-cache-canvases

Zero the height and width of cached canvases before deleting them.
Merge pull request #4950 from fkaelberer/fasterJPEGtransform

Faster JPEG transform
Added getOperatorList to api.js
Merge pull request #4951 from pramodhkp/getoperatorlist

Added getOperatorList to api.js