Python 3 compatibility

### exec -> exec function

```
➜ sudo pip install tarantool

Downloading/unpacking tarantool
  Downloading tarantool-0.3.4.tar.gz
  Running setup.py egg_info for package tarantool
    Traceback (most recent call last):
      File "<string>", line 16, in <module>
      File "/private/tmp/pip_build_root/tarantool/setup.py", line 9
        exec line
                ^
    SyntaxError: invalid syntax
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):

  File "<string>", line 16, in <module>

  File "/private/tmp/pip_build_root/tarantool/setup.py", line 9

    exec line

            ^

SyntaxError: invalid syntax
```

http://docs.python.org/3/library/functions.html#exec



### xrange -> range


```
    import tarantool
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/__init__.py", line 6, in <module>
    from tarantool.connection import Connection
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/connection.py", line 12, in <module>
    from tarantool.request import (
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/request.py", line 12, in <module>
    class Request(object):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/request.py", line 25, in Request
    for val in xrange(0x4000)
NameError: name 'xrange' is not defined
```

http://docs.python.org/3/library/functions.html#range


### StandardError ->  Exception
```
    import tarantool
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/__init__.py", line 6, in <module>
    from tarantool.connection import Connection
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/connection.py", line 11, in <module>
    from tarantool.response import Response
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/response.py", line 8, in <module>
    from tarantool.error import *
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/tarantool/error.py", line 28, in <module>
    class Error(StandardError):
NameError: name 'StandardError' is not defined
```

In Python 2.7, all exceptions are children of StandardError,
and from Python 3 on they descend directly from Exception.


http://docs.python.org/3/library/exceptions.html#exceptions.Exception


```
➜ python --version
Python 3.3.0
```

```
➜ pip --version
pip 1.4.1 from /opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages (python 3.3)
```