Although we'll now end up with only `mustache.js` in the git repo,
being written in ESM syntax, the npm package will still be as before:

- `mustache.js`: UMD, meaning CommonJS, AMD or global scope
- `mustache.mjs`: ESM

None of the recent maintainers has remembered trying to keep the
nuget.org package up to date.

As of writing this, it's over 7 years since the last mustache.js
version got published on nuget (v0.7.2).

Adding to that, there has been no questions asked from the nuget
community about outdated versions.

With the above in mind, we'll remove the nuget spec from our repo
since it only adds to confusion at this point.

Refs https://www.nuget.org/packages/mustache.js/

The git pre-commit hook we've been using the last years to keeping
.version found in `package.json` in sync with the .version field
exposed by the source code, did not handle version numbers often
used for pre-relases like `beta | new` etc.

Therefore making sure it searches for versions that also contains
characters, not only numbers separated by dots. That will make sure
the following is also seen as valid versions: `3.2.0-beta.0`,
whereas before the `-beta` part would cause trouble.

This changes the pre-commit hook that we've used for years to keep the
version value found in `package.json` in sync with the one in
`mustache.js`, to change `mustache.mjs` instead since that's where the
source code lives now.

[spm](https://github.com/spmjs/spm) seems to have been stale for 4 years
and has a deprecation warning in its github repository.

Previously mocha, uglifyjs and jshint used when publishing a new version were ensured / installed by `Rakefile` via the pre-commit git hook. Those modules were automatically installed globally if not present in `$PATH`.

Installing modules globally has one particular downside that we should avoid: we can't ensure developers publishing new mustache.js versions have the same version of these 3rd party modules installed.

If instead we make these modules local dev dependencies, we can ensure which versions are installed, and we make 3rd party dependencies explicit by listing them in `package.json`, rather than in `Rakefile`.

`version` is currently a moot prop since git tags are used instead. More
info at https://github.com/bower/bower.json-spec/commit/a325da3.

Due to eslint changes, pre-commit hook was failing to locate version in
mustache.js due to code using single quotes now, therefore "X.X.X" was
not longer matching, and had to be changed to 'X.X.X'.