Impl. extension of template delimeter expressions

Impl. extension of template delimeter expressions

Implemented "IF", "ELSEIF", "ELSE", "ENDIF", and "INDEX" for templates.

IF is used like: `{{{!IF Variable==SomeString}}}`.
ELSEIF is used like: `{{{!ELSEIF Variable==AnotherString}}}`.
ELSE is used like: `{{{!ELSE}}}`.
ENDIF is used like: `{{{!ENDIF}}}`.
INDEX is used like: `{{{!INDEX ArrayVar[2]}}}`.