添加说明文档，为cangjie层添加单元测试

test/scripts/args_test.lua

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+return (...)

test/scripts/cross_call_get.lua

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+return table.concat(data, ',')

test/scripts/cross_call_set.lua

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+data = {1,2,3}

test/scripts/get_global.lua

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+return tostring(g or 'nil')

test/scripts/io_read_test.lua

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+local s = io.read('*a')
+return s

test/scripts/io_write_test.lua

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+io.write("Data from lua")

test/scripts/mylib.lua

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+function foo() return 42 end

test/scripts/print_test.lua

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+print("Hello Cangjie")

test/scripts/runtime_error.lua

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+error("oops")

test/scripts/set_global.lua

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+g = 123

test/scripts/simple_return.lua

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+return "hello"

test/scripts/syntax_error.lua

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+for i=1,10 print(i) end