Safely override .kind and Buffer improvements

[daogrady]

Only add override modifier to kind property iff any parent class actually has such a property to override.
This change is implicitly tested by having added strict: true to the transpilation tests in tscheck.js.
Fixes #273

Generally, the creation of class members has been streamlined to avoid typos and incorrect order/ combination of modifiers via lib/components.class::createMember instead of concatenating strings manually.

Also streamlined use of Buffer.add to accept scalar strings, array of strings, and functions returning strings, to enable buffer.add(xs) over xs.forEach(x => buffer.add(x)).
Also added buffer.blankLine() to replace the somewhat obscure buffer.add('')