These changes allows the internal template cache to
be customised, either by disabling it complete or
providing a custom implementation of how templates
are cached.

Historically jQuery was seen as an absolute minimal to create
anything with JavaScript. That time has past now that relatively
modern browsers has excellent support for a lot of the things
jQuery helped us with -- at least with the trivial examples shown
in our README.

Therefore removing jQuery usage from our examples as that should
not be a necessary dependency in these examples.

When recently updating the usage examples in the README,
it blooper was introduced where `response.text()` was forgotten
when retrieving a mustache template with `window.fetch()`.

Primarily because [rtype](https://github.com/ericelliott/rtype) seems to
be a stalled project that hasn't gotten updated for 4 years.

Similar more up-to-date definitions can be found in the
TypeScript definitions: [@types/mustache](https://www.npmjs.com/package/@types/mustache).

More and more of the community seems to be encouraging use of
zero-dependency packages. We might as well point that out early
on in our README since that's how mustache.js always has been
and planned to be going forward.

Primarily because the these sections were very given a lot
of attention, high up in the README, where ideally usage and
basic syntax should have priority.

Since TypeScript usage has exploded the last years but this is
package is written in JavaScript, we might at least reference
the external DefinitelyTyped package @types/mustache that has
a somewhat up-to-date set of type definitions for most of the package.

Blooper introduced when making the usage examples in README.md
more modern a couple of days ago, where the example fetching the
mustache template over HTTP, didn't in fact use the fetched template.

In the spirit of keeping the public API of mustache.js as small as
possible for maintainence reasons, the undocumented and un-tested
`.to_html()` method is removed.

The functionality involved, where it can rather invoke an optional
function provided with the result of `.render()`, instead of returning
it as a string like `.render()` does, is something that using projects
very easily can do themselfs -- it does not have to be provided by
mustache.js.