add nodejs and AssemblyScript memory share demo

memshare/.gitignore

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+node_modules/
+package-lock.json
+build/

memshare/README.md

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+# Memory Share Demo
+## Description
+This Demo is using Nodejs for implementation.  
+The main purpose is share memory between Nodejs side and AssemblyScript side.  
+1. after run the demo, it will print:  
+    ```
+    hello world
+    hhllo world
+    ```
+2. the first `hello world` is from the function `trace`, after AS call `trace` function, we get the offset of the string.
+3. the second `hhllo world` is that, after we get the position of string, we can change the value with this offset position. so if AS call `trace` again, actually the value of linear memory has been changed.  
+
+Technically we can use shared memory without limitation, this `trace` function is a string demo, you can also use this method to share objects (need to embed it on Nodejs side) in linear memory.  
+
+## Build
+`npm install`
+## Run Demo  
+`npm run test`

memshare/asconfig.json

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+{
+  "targets": {
+    "debug": {
+      "outFile": "build/debug.wasm",
+      "textFile": "build/debug.wat",
+      "sourceMap": true,
+      "debug": true
+    },
+    "release": {
+      "outFile": "build/release.wasm",
+      "textFile": "build/release.wat",
+      "sourceMap": true,
+      "optimizeLevel": 3,
+      "shrinkLevel": 0,
+      "converge": false,
+      "noAssert": false
+    }
+  },
+  "options": {
+    "bindings": "esm"
+  }
+}

memshare/assembly/index.ts

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+export function test(): void {
+    let str = "hello world";
+    trace(str, str.length);
+}

memshare/assembly/tsconfig.json

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+{
+  "extends": "assemblyscript/std/assembly.json",
+  "include": [
+    "./**/*.ts"
+  ]
+}

memshare/package.json

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+{
+  "name": "as_demo",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "npm run asbuild && node run.cjs",
+    "asbuild:debug": "asc assembly/index.ts --target debug ",
+    "asbuild:release": "asc assembly/index.ts --target release ",
+    "asbuild": "npm run asbuild:debug && npm run asbuild:release",
+    "start": "npx serve ."
+  },
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "assemblyscript": "0.20.19"
+  },
+  "type": "module",
+  "exports": {
+    ".": {
+      "import": "./build/release.js",
+      "types": "./build/release.d.ts"
+    }
+  }
+}

memshare/run.cjs

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+const fs = require('fs');
+const wasmBuffer = fs.readFileSync('build/debug.wasm');
+
+const imports = {};
+imports.env = imports.env || {};
+var sharedMemory = new WebAssembly.Memory({ initial: 1 });//request one page memory
+var globalOffset=0;
+Object.assign(imports.env, {
+  memory: sharedMemory,
+  trace: function (offset, length) {
+    var bytes = new Uint8Array(sharedMemory.buffer, offset, length*2);
+    globalOffset = offset;
+    var string = new TextDecoder('utf8').decode(bytes);
+    console.log(string);
+  },
+  abort(_msg, _file, line, column) {
+    console.error("abort called at index.ts:" + line + ":" + column);
+  }
+});
+
+WebAssembly.instantiate(wasmBuffer, imports).then(wasmModule => {
+  const { test,memory } = wasmModule.instance.exports;
+  sharedMemory = memory;
+  test();
+  var bytes = new Uint8Array(sharedMemory.buffer, globalOffset, 6);
+  bytes[2] = 104;
+  test();
+});