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 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 thoroughly

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

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 thoroughly

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

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

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

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

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

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Python: add Sphinx doc project