Python: decouple Python iface from native binding

With this patch, all the SWIG stuff is isolated into
nativebt.i, whereas the real Babeltrace Python interface
is plain Python in babeltrace/bt.py.

The Babeltrace Python binding is now a Python package, but
backward compatibility with the original module is ensured
by importing all public symbols from the bt module in the
package itself (__init__.py), which is named like the
original module, babeltrace.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: remove explicit inheritance from object

This is a Python 3 binding, and all classes are new-style
classes in Python 3, so there is no need to inherit from object
explicitly.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: bt.py: PEP 8 + improve readability

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: remove useless 'return None'

A Python function's default return value is None already.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document TraceCollection

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document print_format_list()

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: bt: do not expose ClockType

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document TraceHandle

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document CTFStringEncoding

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document ByteOrder

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document CTFTypeId

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document CTFScope

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document Event

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document FieldError

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document EventDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document FieldDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document IntegerFieldDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document EnumerationFieldDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document ArrayFieldDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: document SequenceFieldDeclaration

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>