..simply forgot that when preparing the v4.2.0 release

Added changelog for about to be published version with migration guides
for changes that might be considered unexpected.

I made most of the `CHANGELOG.md` changes 2 August, but did not push the
version to npm until 7 August. Updating the changelog just in case anyone
updates and looks back on the changelog for clues of when things happen.

I'm sorry. :see_no_evil:

This reverts commit 2f51083565. Util is
not yet configurable, so issue links point to `mocha`.

The goal is to reduce the number of files downloaded by ignoring the test directory

Removed cache* functions altogether. mustache.parse is all that's
really needed.

This commit allows pre-compiled templates to be executed without
keeping the original template around. It is still required when using
higher-order functions.

Fixes #262

Fixes #247

Text tokens now accurately reflect their content's exact position
in the original template.