types: support working with binary for Python 3

[DifferentialOrange]

Merge after #213

This is a breaking change.

Before this patch, both bytes and str were encoded as mp_str. It was
possible to work with utf and non-utf strings, but not with
varbinary (mp_bin) [1]. This patch adds varbinary support for Python 3
by default. With Python 2 the behavior of the connector remains the same.

Before this patch:

• encoding="utf-8" (default)

  Python 3	->	Tarantool	->	Python 3
  str	->	mp_str (string)	->	str
  bytes	->	mp_str (string)	->	str
  		mp_bin (varbinary)	->	bytes

• encoding=None

  Python 3	->	Tarantool	->	Python 3
  bytes	->	mp_str (string)	->	bytes
  str	->	mp_str (string)	->	bytes
  		mp_bin (varbinary)	->	bytes

Using bytes as key was not supported by several methods (delete,
update, select).

After this patch:

• encoding="utf-8" (default)

  Python 3	->	Tarantool	->	Python 3
  str	->	mp_str (string)	->	str
  bytes	->	mp_bin (varbinary)	->	bytes

• encoding=None

  Python 3	->	Tarantool	->	Python 3
  bytes	->	mp_str (string)	->	bytes
  str	->	mp_str (string)	->	bytes
  		mp_bin (varbinary)	->	bytes

Using bytes as key are now supported by all methods.

Thus, encoding="utf-8" connection may be used to work with
utf-8 strings and varbinary and encodine=None connection
may be used to work with non-utf-8 strings.

This patch does not add new restrictions (like "do not permit to use
str in encoding=None mode because result may be confusing") to preserve
current behavior (for example, using space name as str in schema
get_space).

1. Introduce VARBINARY field type tarantool#4201

Closes #105

[DifferentialOrange]

Note: test this PR rebased on #213 to ensure different msgpack package version compatiility

[Totktonada]

I have no objections, just several suggestions.

LGTM.

[Totktonada]

I glanced over the changes and I'm completely okay here. Please, finish the review with Sergey and proceed.

[ligurio]

Thanks for the patch!

LGTM