Add example: snake

_examples/snake/README.md

+# Pkg: _examples/snake
+
+TODO

_examples/snake/src/canvas/canvas.wa

+# 版权 @2022 凹语言 作者。保留所有权利。
+
+fn Test(){
+	println(42)
+}
\ No newline at end of file

_examples/snake/src/main.wa

+# 版权 @2019 凹语言 作者。保留所有权利。
+
+import "snake/canvas"
+
+fn main() {
+	canvas.Test()
+}

_examples/snake/wa.mod.json

+{
+	"name": "_examples/snake",
+	"pkgpath": "snake",
+	"version": "0.0.1",
+	"authors": ["author", "author2"],
+	"description": "module description",
+	"readme": "README.md",
+	"homepage": "",
+	"repository": "",
+	"license": "",
+	"license_file": "",
+	"keywords": [],
+	"categories": []
+}