* add .TemplateData property to data in order to populate template <title> tags with the compiled subject value
* update all templates
* re-enable integration test and update implementation to check changes
* chore: fmt
* add HiddenSubject template func and update text templates
* slight performance improvement, only execute subject template once
* update template I missed
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Co-authored-by: Gilles De Mey <gilles.de.mey@gmail.com>
// hiddenSubjectTemplateFunc sets the subject template (value) on the map represented by `.Subject.` (obj) so that it can be compiled and executed later.
// It returns a blank string, so there will be no resulting value left in place of the template.
// subjectTemplateFunc does the same thing has hiddenSubjectTemplateFunc, but in addition it executes and returns the subject template using the data represented in `.TemplateData` (data)
// This results in the template being replaced by the subject string.