New creates a TemplateData object which supports the following user-defined functions: - env KEY replace `env KEY` with the value of `KEY` read from ENV - hostname replace `hostname` with the value of os.Hostname() - value KEY replace `value KEY` with the value of `KEY` read from Stores assigned to the TemplateData object.

WithStores sets Stores from which data is read into TemplateData.

TemplateData provides data for replacing templates.