RFE: debug=true flag

I know this defeats the performance goals ... but would be fantastic to add an option:

debug=true (default is false)

which will output an error code in the HTML or log if:
- TPL not found on instantiation of NTPL object
- base tmpl not found when inheriting
- line # reporting and stack trace are optional, usually not needed (maybe part of verbosity option)

Please keep up the good work!

Start by tracing NTPL object instantiation and the template-inheritance path to identify where missing templates are handled. Determine how a debug option would be configured and whether diagnostics belong in HTML, logs, or both. Done means the requested missing-template cases produce error codes when debug=true while remaining silent by default, with optional line and stack-trace reporting defined.

Written by the indexing model from the issue text.