A TLObject class has been added, as well as a method for tokenizen .tl files.
A TLObject can be created by simply calling `TLObject.from_tl(tl_line)`,
this will tokenize the .tl line and return a new TLObject with all
the required properties extracted.
Also added another method to load .tl files and yield TLObjects, including
a SourceBuilder that can be later used to generate Python code.
