Create a new MTProtoSender structure and its foundation

This means that the TcpClient and the Connection (currently only
ConnectionTcpFull) will no longer be concerned about handling
errors, but the MTProtoSender will.

The foundation of the library will now be based on asyncio.

telethon/network/connection/tcpfull.py

@@ -20,7 +20,7 @@ class ConnectionTcpFull(Connection):
         self.read = self.conn.read
         self.write = self.conn.write
 
-    def connect(self, ip, port):
+    async def connect(self, ip, port):
         try:
             self.conn.connect(ip, port)
         except OSError as e:
@@ -37,13 +37,13 @@ class ConnectionTcpFull(Connection):
     def is_connected(self):
         return self.conn.connected
 
-    def close(self):
+    async def close(self):
         self.conn.close()
 
     def clone(self):
         return ConnectionTcpFull(self._proxy, self._timeout)
 
-    def recv(self):
+    async def recv(self):
         packet_len_seq = self.read(8)  # 4 and 4
         packet_len, seq = struct.unpack('<ii', packet_len_seq)
         body = self.read(packet_len - 12)
@@ -55,7 +55,7 @@ class ConnectionTcpFull(Connection):
 
         return body
 
-    def send(self, message):
+    async def send(self, message):
         # https://core.telegram.org/mtproto#tcp-transport
         # total length, sequence number, packet and checksum (CRC32)
         length = len(message) + 12