Special values of ln_

[cbmarini]

At the moment special values for the trigonometric functions are treated separately, i.e. sin_(pi_/6) evaluates to 5.0e-01. However, for the other functions the argument must first be evaluated manually. For instance:

#Startfloat 64
L F = ln_(cos_(1));
Argument ln_;
	Evaluate;
EndArgument;
Evaluate;
Print;
.end

   F =
       - 6.15626470386014262147e-01;

This is nice as it gives users full control over the evaluation process.
However, this raises a question about how to handle simpler known expressions like ln_(ee_). Should this also require explicit evaluation of the argument (as with ln_(cos_(1))), or should it automatically reduce to 1 (like sin_(pi_/6) does)?