reorganize the library into three folders lib, contrib and core

Write unittests with pytest
Make all functions and method signatures as keyword only arguments

tests/unittests/test_order.py

@@ -0,0 +1,27 @@
+from aiomql.lib.order import Order
+
+
+class TestOrder:
+    async def test_check(self, sell_order):
+        order = Order(**sell_order)
+        check = await order.check()
+        assert check.retcode == 0
+
+    async def test_send(self, buy_order):
+        order = Order(**buy_order)
+        send = await order.send()
+        assert send.retcode == 10009
+
+    async def test_margin(self, buy_order):
+        order = Order(**buy_order)
+        margin = await order.calc_margin()
+        assert margin is not None
+        assert margin > 0
+        assert isinstance(margin, float)
+
+    async def test_profit(self, buy_order):
+        order = Order(**buy_order)
+        profit = await order.calc_profit()
+        assert profit is not None
+        assert profit > 0
+        assert isinstance(profit, float)