Add dataset templating support

[mikee47]

This PR extends templated streaming to support formatting of large datasets.
It is used by #1579 to provide a mechanism for streaming directory listings in various formats.

Upgrade TemplateStream

• Malformed template data can cause lockup waiting for next input when there isn't any.
• Add output enable control to support filtering
• Allow spaces in tag names, increase max length to 128
• Add evaluate method to enable support for extended tag parsing
• Add optional owned parameter to TemplateStream constructor for situations where caller is responsible for allocation
• Allow TemplateStream to be rewound: implement seekFrom
• Add option to use double braces {{ }} - necessary for JSON

Add class-based support for escaping/formatting strings (html, json, etc)

• Base Formatter class, headers and standard/html/json within Format namespace

Add SectionStream class

• Presents each marked section within a source stream as a separate stream
• Sections are identified by index and can be selected to allow repeating of sections, etc. as required

Add SectionTemplate class to support dataset reporting

• Adds basic expression parsing with conditionals, built-in functions, etc.
• Uses SectionStream to support typical reports with a header/content/footer. The content section is repeated for each record.

Add separate TemplateStream test module, with more tests