Point typedoc at matrix.ts, not index.ts (matrix-org#3239)

This gets rid of the rather pointless "default" module in the generated docs.

tsconfig.json

@@ -12,7 +12,7 @@
     },
     "include": ["./src/**/*.ts", "./spec/**/*.ts"],
     "typedocOptions": {
-        "entryPoints": ["src/index.ts"],
+        "entryPoints": ["src/matrix.ts"],
         "excludeExternals": true,
         "out": "_docs"
     }