add js build tool and demo page

.gitignore

@@ -1,3 +1,5 @@
+dist/
+
 # Compiled class file
 *.class
 
@@ -64,3 +66,6 @@ node_modules/
 
 # TernJS port file
 .tern-port
+
+# Build cache
+.parcel-cache

.nvmrc

@@ -0,0 +1 @@
+lts/fermium

.swcrc

@@ -0,0 +1,3 @@
+{
+  "minify": true
+}

demo/index.css

@@ -0,0 +1,67 @@
+body {
+  font-family: -apple-system, BlinkMacSystemFont, sans-serif;
+  margin: 2rem auto;
+  background-color: #ececef;
+  max-width: 100%;
+  width: 640px;
+}
+
+.MiniApp {
+  box-shadow: -2px 2px 4px #dadada;
+  border-radius: 8px;
+  border: 1px solid #cecece;
+  border-top-width: 28px;
+  padding: 2rem;
+  max-width: 100%;
+  position: relative;
+}
+
+.MiniApp::after {
+  content: "○ ○ ○";
+  position: absolute;
+  top: -24px;
+  left: 6px;
+  font-weight: bold;
+  color: #aaa;
+  font-size: 14px;
+}
+
+.MiniApp-button {
+  border-width: 2px;
+  border-style: solid;
+  border-radius: 100px;
+  border-color: #ccc;
+  background-color: #fff;
+  cursor: pointer;
+  padding: 0 1em;
+  height: 2.5rem;
+  display: inline-flex;
+  align-items: center;
+}
+
+.MiniApp-button + .MiniApp-button,
+.MiniApp-input + .MiniApp-input,
+.MiniApp-input + .MiniApp-button,
+.MiniApp-button + .MiniApp-input {
+  margin-left: 10px;
+}
+
+.MiniApp-input {
+  border-radius: 4px;
+  border-width: 2px;
+  background-color: #fff;
+  border-color: #ccc;
+  border-style: solid;
+  height: 2.5rem;
+  display: inline-flex;
+  align-items: center;
+  position: relative;
+  padding: auto 0.5rem;
+}
+
+.MiniApp-flex-row {
+  display: flex;
+  flex-direction: row;
+  flex-wrap: wrap;
+  align-items: center;
+}