Fix some incompatibilities with strict mode

[DannyBen]

As reported in #445 - it appears that some rendering views are incompatible with set -u strict mode, and cause an unbound variable in the rendered script. This PR fixes it and improves tests to cover this use case.

Notable changes:

1. Some views and libraries were changed to avoid unbound variable by changing $arg['something'] to ${arg['something']:-} (or a similar syntax as appropriate).
2. The examples spec was changed to enable strict mode before running to ensure all examples are generated in strict mode and pass tests.