optscript: minor issues

[masatake]

Interpreter:

• [ ] provide the way to fill language specific fields
• [ ] provide the way to create anonymous tags
• [ ] provide accessors for implementation field
• [ ] revise the original {_field=} feature
• [ ] _strrpbrk
• [ ] write a tutorial
• [ ] options fo listing error types.
• [x] provide operators to specify locations (_matchloc)
• [ ] accessor for table execution stack
• [x] provide the way to run guest parsers (_makepromise)
• [x] provide accessors for access field (:access, access:)
• [ ] provide accessors for file field
• [ ] provide accessors for pattern field
• [ ] implement \0
• [ ] Assert() alike operator

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Improve parsers:

• [x] rewrite puppetManifest parser. See #2974. (partially done)
• [x] operator for setting placeholder flag (in progress #3027)
• [ ] Implement Vue
• [ ] Imporove Elm parser