Skip new interpolation test and optional inheritance part of the spec

There is a small typo in test/mustache-spec-test.js.

Should read `skipped` rather than `skiped`.

As referenced in this issue:
https://github.com/janl/mustache.js/issues/562

Partials aren't indented as per the spec:
https://github.com/mustache/spec/blob/master/specs/partials.yml#L13-L15

This adds indentation tracking for partials and applies them to the
first instance of a partial on a line (to not indent inline partials
which would violate a different part of the spec).

In an effort of ensuring consistent code style in test files as with
the "production" source code, we should run eslint as part of the
`$ npm test` script as well.

Most of the related fixes was done by `eslint` using the `--fix` argument.

Only special configuration tweaks for tests compared to the other
source code, is to allow functions declaration without names. The
rationale for allowing that in tests, is that the important reason we
have them in the source code (proper stacktraces) aren't as important
in test files.