introduce eager evaluation (#3587)

README.md

@@ -631,7 +631,10 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 - `drop_debugger` (default: `true`) -- remove `debugger;` statements
 
-- `evaluate` (default: `true`) -- attempt to evaluate constant expressions
+- `evaluate` (default: `true`) -- Evaluate expression for shorter constant
+  representation. Pass `"eager"` to always replace function calls whenever
+  possible, or a positive integer to specify an upper bound for each individual
+  evaluation in number of characters.
 
 - `expression` (default: `false`) -- Pass `true` to preserve completion values
   from terminal statements without `return`, e.g. in bookmarklets.