Added constant-only functions min, max, if. Improved handling of constant-only functions.

docs/lang/literals.md

@@ -199,7 +199,7 @@ Fields of arithmetic, pointer and enum types are declared using normal expressio
 Fields of struct types are declared using struct constructors.
 Fields of union types cannot be declared.
 
-What might be useful is the fact that the compiler allows for built-in trigonometric functions
+What might be useful is the fact that the compiler allows for certain built-in functions
 in constant expressions only:
 
 * `sin(x, n)` – returns _n_·**sin**(*x*π/128)
@@ -208,3 +208,7 @@ in constant expressions only:
 
 * `tan(x, n)` – returns _n_·**tan**(*x*π/128)
 
+* `min(x,...)` – returns the smallest argument
+
+* `max(x,...)` – returns the largest argument
+

docs/lang/preprocessor.md

@@ -135,7 +135,7 @@ The `if` function returns its second parameter if the first parameter is defined
     #infoeval if(0, 400, 500)
 
 TODO   
-`not`, `lo`, `hi`, `+`, `-`, `*`, `|`, `&`, `^`, `||`, `&&`, `<<`, `>>`,`==`, `!=`, `>`, `>=`, `<`, `<=`
+`not`, `lo`, `hi`, `min`, `max` `+`, `-`, `*`, `|`, `&`, `^`, `||`, `&&`, `<<`, `>>`,`==`, `!=`, `>`, `>=`, `<`, `<=`
 
 The following Millfork operators and functions are not available in the preprocessor:  
 `+'`, `-'`, `*'`, `<<'`, `>>'`, `:`, `>>>>`, `nonet`, all the assignment operators