Reorganize language bindings

* Move rust binding: lib/binding -> lib/binding_rust
* Move wasm bindinig: lib/web -> lib/binding_web
* Add wasm readme

lib/binding_web/README.md

@@ -0,0 +1,105 @@
+tree-sitter.wasm
+================
+
+[![Build Status](https://travis-ci.org/tree-sitter/tree-sitter.svg?branch=master)](https://travis-ci.org/tree-sitter/tree-sitter)
+
+Wasm bindings to the [Tree-sitter](https://github.com/tree-sitter/tree-sitter) parsing library.
+
+### Basic Usage
+
+You can either load the library as a standalone script:
+
+```html
+<script src="/public/js/tree-sitter.js"/>
+
+<script>
+  const Parser = window.TreeSitter;
+  Parser.init().then(() => { /* the library is ready */ });
+</script>
+```
+
+or using a packaging system like Webpack:
+
+```js
+const Parser = require('tree-sitter');
+Parser.init().then(() => { /* the library is ready */ });
+```
+
+Create a parser:
+
+```js
+const parser = new Parser;
+```
+
+Then assign a language to the parser. Tree-sitter languages are packaged as individual `.wasm` files:
+
+```js
+const JavaScript = await Parser.Language.load('/path/to/tree-sitter-javascript.wasm');
+parser.setLanguage(JavaScript);
+```
+
+Now you can parse source code:
+
+```js
+const sourceCode = 'let x = 1; console.log(x);';
+const tree = parser.parse(sourceCode);
+```
+
+and inspect the syntax tree.
+
+```javascript
+console.log(tree.rootNode.toString());
+
+// (program
+//   (lexical_declaration
+//     (variable_declarator (identifier) (number)))
+//   (expression_statement
+//     (call_expression
+//       (member_expression (identifier) (property_identifier))
+//       (arguments (identifier)))))
+
+const callExpression = tree.rootNode.child(1).firstChild;
+console.log(callExpression);
+
+// { type: 'call_expression',
+//   startPosition: {row: 0, column: 16},
+//   endPosition: {row: 0, column: 30},
+//   startIndex: 0,
+//   endIndex: 30 }
+```
+
+### Editing
+
+If your source code *changes*, you can update the syntax tree. This will take less time than the first parse.
+
+```javascript
+// Replace 'let' with 'const'
+const newSourceCode = 'const x = 1; console.log(x);';
+
+tree.edit({
+  startIndex: 0,
+  oldEndIndex: 3,
+  newEndIndex: 5,
+  startPosition: {row: 0, column: 0},
+  oldEndPosition: {row: 0, column: 3},
+  newEndPosition: {row: 0, column: 5},
+});
+
+const newTree = parser.parse(newSourceCode, tree);
+```
+
+### Parsing Text From a Custom Data Structure
+
+If your text is stored in a data structure other than a single string, you can parse it by supplying a callback to `parse` instead of a string:
+
+```javascript
+const sourceLines = [
+  'let x = 1;',
+  'console.log(x);'
+];
+
+const tree = parser.parse((index, position) => {
+  let line = sourceLines[position.row];
+  if (line) return line.slice(position.column);
+});
+```