Add README and move metrics script.

README.md

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+Wren is a *small, clean, fast, class-based scripting language.* Think Smalltalk
+in a Lua-sized package.
+
+```dart
+IO.print("Hello, world!")
+
+class Wren {
+  adjectives = ["sm\nall", "clean", "fast"]
+  languageType {
+    "scripting"
+  }
+}
+```
+
+ *  **Wren is small.** The codebase is under 4,000 semicolons which keeps the
+    language and libraries small enough to fit in your head. You can skim
+    [the whole thing][src] in one sitting.
+
+ *  **Wren is clean.** The codebase is *small*, but not *dense*. It is readable
+    and [lovingly-commented][nan]. It's written in warning-free standard C99.
+
+ *  **Wren is fast.** A fast single-pass compiler to tight bytecode, and a
+    compact object representation help Wren [compete with other dynamic
+    languages][perf].
+
+ *  **Wren is class-based.** There are lots of scripting languages out there,
+    but many have unusual or non-existent object models. Wren places
+    [classes][] front and center.
+
+ *  **Wren is a scripting language.** Wren is intended for embedding in
+    applications. It has no dependencies, a small standard library,
+    and [an easy-to-use C API][embedding].
+
+[src]: https://github.com/munificent/wren/tree/master/src
+[nan]: https://github.com/munificent/wren/blob/46c1ba92492e9257aba6418403161072d640cb29/src/wren_value.h#L378-L433
+[perf]: http://munificent.github.io/wren/performance.html
+[classes]: http://munificent.github.io/wren/classes.html
+[embedding]: http://munificent.github.io/wren/embedding-api.html