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/common.py

@@ -1,5 +1,14 @@
 """
 This module holds the abstract `Connection` class.
+
+The `Connection.send` and `Connection.recv` methods need **not** to be
+safe across several tasks and may use any amount of ``await`` keywords.
+
+The code using these `Connection`'s should be responsible for using
+an ``async with asyncio.Lock:`` block when calling said methods.
+
+Said subclasses need not to worry about reconnecting either, and
+should let the errors propagate instead.
 """
 import abc
 from datetime import timedelta
@@ -23,7 +32,7 @@ class Connection(abc.ABC):
         self._timeout = timeout
 
     @abc.abstractmethod
-    def connect(self, ip, port):
+    async def connect(self, ip, port):
         raise NotImplementedError
 
     @abc.abstractmethod
@@ -41,7 +50,7 @@ class Connection(abc.ABC):
         raise NotImplementedError
 
     @abc.abstractmethod
-    def close(self):
+    async def close(self):
         """Closes the connection."""
         raise NotImplementedError
 
@@ -51,11 +60,11 @@ class Connection(abc.ABC):
         raise NotImplementedError
 
     @abc.abstractmethod
-    def recv(self):
+    async def recv(self):
         """Receives and unpacks a message"""
         raise NotImplementedError
 
     @abc.abstractmethod
-    def send(self, message):
+    async def send(self, message):
         """Encapsulates and sends the given message"""
         raise NotImplementedError