Saner handling of check preparation and better execution of several suites.

The main internal change of this release is the use of a generic metadata mechanism which allows to attach arbitrary metadata to a test and using this mechanism during generation of HTML reports for suites. This is technically an incompatible change against the 3.x series.

Most prominent user facing change is the ability to provide mock services, either standalone via the "mock" subcommand of cmd/ht or during suite execution.

The main stuff in this release are working load/throughput tests.

This is a major and incompatible release.

The major change is in reading suites and tests from disk: The new format uses hjson and a different structure:

• Hjson (http://hjson.org) is even more human friendly than JSON5 (and the JSON5 package used had bugs)
• The different parameters controlling a test execution (polling, trying, sleeping) have been consolidated into a new field Execution.
• Some inconsistencies between checks and extractors have been cleaned.
• Capturing Screenshots has been improved.
• Added possibility to check JSON-in-JSON, and some edge case fixes.
• Variable handling works now much better and clearer und suites.
• Test "unrolling" is replaced by parameterized tests (i.e. tests which variables which are settable during inclusion of the test in the suite).
• The generated HTML reports no longer require JQuery and are a bit nicer.
• The documentation is now baked in: ht doc Screenshot now shows the information about the Screenshot test, even if neither go nor the ht sources are installed.

• Provide new check: CustomJS which executes custom JavaScript code to check the response.
• Provide new extractor: JSExtractur which uses custom JavaScript code to extract values.
• Fix reporting ERROR if just teardown tests fail

Major stuff:

• Logical combinations of checks (OR and NOR) via the AnyOne and None checks.
• Easier testing of redirect chains via the RedirectChain check.
• Better color histogram fingerprinting.
• Fixes and improvements to the recorder.
• Minor bugfixes and improvements.

The change to color histogram image fingerprinting is a backwards incompatible
change: You will have to regenerate the fingerprints with the new version.

More subcommands, working ValidHTML check, general cleanup, better check failure reporting.

• Include image fingerprinting and reconstruction as subcommand into cmd/ht.
• Allow recording of tests via a reverse proxy.
• Add Resilience check to torture a resource.
• Several bug fixes.

Added Latency and Sorted checks as well as some bugfixes.

Fixes some bugs (HEAD request with gzip, missing cookies during Link checking and a panic).