Changes `for` directive syntax to `data-for="planet in planets"`
Renames `ref` directive to `refer` directive to be more consistent with imperative style names used for other directives
Changes the syntax of the `set` directive from `data-set="a=42"` to `data-set="a to 42"`
Alters error attributes to have attribute with a name suffixed by error type and a value of error data e.g 'data-error-required="param"'
Changes `par` directive syntax and refactors and reorganises associated code.
Changes `exec` directive syntax and refactors it into a `Stencil::Execute` struct.
Changes `include` directive syntax and refactors it into a `Stencil::Include` struct. Also a `Stencil::Set` struct.