feat: Added mustache templating.

mustache/spec/TESTING.md

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+Testing your Mustache implementation against this specification should be
+relatively simple.  If you have a readily available testing framework on your
+platform, your task may be even simpler.
+
+In general, the process for each `.yml` file is as follows:
+
+1. Use a YAML parser to load the file.
+
+2. For each test in the `tests` array:
+
+    1. Ensure that each element of the `partials` hash (if it exists) is
+       stored in a place where the interpreter will look for it.
+
+    2. If your implementation will not support lambdas, feel free to skip
+       over the optional `~lambdas.yml` file.
+
+       Otherwise, ensure that each member of `data` tagged with `!code` is
+       properly processed into a language-specific lambda reference.
+
+       * e.g. Given this YAML data hash:
+
+         `{ x: !code { ruby: 'proc { "x" }', perl: 'sub { "x" }' } }`
+
+         a Ruby-based Mustache implementation would process it such that it
+         was equivalent to this Ruby hash:
+
+         `{ 'x' => proc { "x" } }`
+
+       * If your implementation language does not currently have lambda
+         examples in the spec, feel free to implement them and send a pull
+         request.
+
+       * The JSON version of the spec represents these tagged values as a
+         hash with a `__tag__` key of `code`.
+
+    3. Render the template (stored in the `template` key) with the given
+       `data` hash.
+
+    4. Compare the results of your rendering against the `expected` value;
+       any differences should be reported, along with any useful debugging
+       information.
+
+       * Of note, the `desc` key contains a rough one-line description of
+         the behavior being tested – this is most useful in conjunction with
+         the file name and test `name`.