Add CLI definitions; CLI restructure

cli/README.md

@@ -0,0 +1,48 @@
+Compiler frontend for node.js
+=============================
+
+Usage
+-----
+
+For an up to date list of available command line options, see:
+
+```
+$> asc --help
+```
+
+API
+---
+
+The API accepts the same options as the CLI but also lets you override stdout and stderr and/or provide a callback. Example:
+
+```js
+const asc = require("assemblyscript/cli/asc");
+asc.main([
+  "myModule.ts",
+  "--binaryFile", "myModule.wasm",
+  "--optimize",
+  "--sourceMap",
+  "--measure"
+], {
+  stdout: process.stdout,
+  stderr: process.stderr
+}, function(err) {
+  if (err)
+    throw err;
+  ...
+});
+```
+
+Available command line options can also be obtained programmatically:
+
+```js
+const options = require("assemblyscript/cli/asc.json");
+...
+```
+
+You can also compile a source string directly, for example in a browser environment:
+
+```js
+const { binary, text, stdout, stderr } = asc.compileString(`...`, { optimize: 2 });
+...
+```