MSON AST origin. MSON parser origin.

This commit also includes following:

- Implicit use of Value<T>::value_type in element value helper
- Rename ValueType to DataType for better clarity
- Signature parser origin, MSON element parser origin.
- Add checking & warnings to the signature parser

    In addition the signature parser is now of standard-parser grade consuming
node iterators and parser data. Also the signature parser now returns any
remaining multiline content.

- Support for `-escaped signature variables
- SectionTraits origin, singleton sections check origin
- MSON element signature parsing completed
- Fix wrong copy-pasted test, remove unimplemented property parser tests
- Rename Signature Trait "traits" to "specifiers"
- Array value parsing
- Finished element signature parsing
- Finalized MSON property signature parsing
- Context for nested sections & descriptions

    Add context to nestedSectionType() and isDescriptionNode() to be able
    process MSON context-sensitive nested sections

- Nested MSON elements parsing
- Properties section parsing
- Object parsing
- Complex property test
- Update to latest shared/refactor-integration changes
- Property only required specifier, templated properties
- Inferred array element type parsing