Class for Template Evaluation: bare-bones counterpart of the Python library "Jinja"
    
    
DEPENDENCIES:  None

USAGE EXAMPLES:
 

    1) simple field substitution:
            "Dear {{name}}, see you on {{day}}"  .  This is Jinja-like (different delimeters may be requested)

            
    2) if/then/else constructs:
    
        { [test] [if-branch string] [else-branch string] }
        
        where test can be: 1) a field (true if not null) ; or 2) "field=string"
        
        Example 1:  "{ [phone] [are you still at {phone}?] [I lack your phone #] }"
        
        Example 2:  "{ [site=c] [some name] [some other name] }"

        
    3) pre-registered, site-provided (NOT user-provided!), functions:
    
        $templ_eval->registerFunction("foo");        // foo() become Registed Function 1 for this site
        
        Example: "Go to link {RF(1, {productID})}"

public  $errors = "";       // The last error message, if any

    public function setTags($openTag, $closeTag)
    // To replace the default tags, if desired

    
    
    
    public function  evaluateTemplate($template, $replaceArray, $outputErrors = true)
    /*  Example of template:  "Dear {{name}}, see you on {{day}}!"
        Example of replaceArray:  array("name" => "Valerie" , "city" => "SF")
        
        Case-sensitive.
     */

    
    
    function exactStringDisplay($str, $caption = "String")
    /*
        This function is just for debugging.
        
        Assemble and return the HTML to display, inside a boxed div element, the given string EXACTLY as it is, 
        without any of the usual HTML printing substitutions.  
        For example "one<br><b>two</b>" will show up exactly as composed.
   */