Implemented init and write code on TLObjects Generator

The code generated by the generator now classifies the output files
in their corresponding categories, also writing their __init__(...)
with documented arguments, and the on_send(...) method

parser/source_builder.py

@@ -1,13 +1,18 @@
+from io import StringIO
+
 
 class SourceBuilder:
     """This class should be used to build .py source files"""
 
-    def __init__(self, indent_size=4):
+    def __init__(self, out_stream=None, indent_size=4):
         self.current_indent = 0
         self.on_new_line = False
         self.indent_size = indent_size
 
-        self.buffer = []
+        if out_stream is None:
+            self.out_stream = StringIO()
+        else:
+            self.out_stream = out_stream
 
     def indent(self):
         self.write(' ' * (self.current_indent * self.indent_size))
@@ -15,9 +20,10 @@ class SourceBuilder:
     def write(self, string):
         if self.on_new_line:
             self.on_new_line = False  # We're not on a new line anymore
-            self.indent()
+            if string.strip():  # If the string was not empty, indent; Else it probably was a new line
+                self.indent()
 
-        self.buffer += list(string)
+        self.out_stream.write(string)
 
     def writeln(self, string=''):
         self.write(string + '\n')
@@ -32,7 +38,12 @@ class SourceBuilder:
         self.writeln()
 
     def __str__(self):
-        if self.buffer:
-            return ''.join(self.buffer)
-        else:
-            return ''
+        self.out_stream.seek(0)
+        return self.out_stream.read()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.out_stream.flush()
+        self.out_stream.close()