Expose simplify in the Python and Node bindings

Config(simplify=...) / property in Python; simplify option in Node,
with the tolerance documented in .pyi, index.d.ts, and both READMEs.
The Node README's option list also catches up with the clustering
rename and the binary/watershed options, and test.js drops the stale
colorMode key (silently ignored since the rename, so its bw assertion
was testing the default path) and asserts simplify shrinks output.

nodejs/index.d.ts

@@ -13,6 +13,8 @@ export interface Options {
   lengthThreshold?: number;
   maxIterations?: number;
   spliceThreshold?: number;
+  /** Curve simplification tolerance in px (omit = off; try 1-2.5). */
+  simplify?: number;
   pathPrecision?: number;
   /** Fixed palette: `#rrggbb` strings. */
   palette?: string[];