ES6 test functions in multi-line strings

This updates the build script, allowing it to interpret ES6 code expressed in function comments instead of concatenated strings (see #190 iscussion) - which is then wrapped in try-catch, eval() and test() structures automatically.

Also, the runtime script has been updated to unwrap those same structures for the tooltip preview, making the resulting display cleaner - lacking even the test() call wrapper.

Only some ES6 and non-standard tests have been converted to make use of this format, for the moment. The remaining tests are the subjects of various pull-requests currently. If those other requests are resolved, conversion of those tests may then be done.

NOTE: as this drastically affects the output of all HTML files, they have not been included in this commit, to allow branch-merging to pass smoothly. A new build commit will thus have to be done after the merge.
We would literally just have to use something like `scriptEl.getAttribute('data-source')` instead of `scriptEl.innerHTML` followed by all the parsing.