Feature tests analysis

[flbulgarelli]

Exposing new interpreter-based test analysis through CLI and JS API.

Also, I opted-in the remaining mandatory options from the CLI.

Pending:

• Add some tests
• Actually test it with ghcjs build. Tested in Issue #217 info update #218
• Add docs
• Refactor TestAnalyzer, Runner, and Testsmodules whose separation has become less clear after this change.
• Implement the proposed interpreter-flags. This is mostly outside the scope of this PR, but I wanted to already share my thoughts 😛 See Implement interpreter flags #216
• Allow test code and extra-code to be specified separately from cli.

[flbulgarelli]

We should document that now mulang

• can run tests
• that only a small subset of imperative programming is supported by now
• that tests can come with optional extra code
• that tests can be extracted from source sample
• that tests can be written in both python and javascript, by now
• that only a small subset of a test framework is supported by now.

[julian-berbel]

👏

[flbulgarelli]

With latest commit, I converted this PR into a backward-compatible change. See #211