Bump version number

Next version will be 0.4.0.
updated requirements
updated tests for TestRealRedis test-case
wake up tests: redis 2.7.6 compatibility
setnx implementation complying with test_set_should_accept_nx
renamed test method
expiring keys support
set px implementation
implemented set xx
refactorings, integrating expiration feature into setex, implemented psetex
implemented expire
implemented expireat
implemented ttl
Pep8 formatting
Tag tests that sleep as slow
Small pep8 fixes
Merge branch 'vladignatyev-master'

* vladignatyev-master:
  Small pep8 fixes
  Tag tests that sleep as slow
  Pep8 formatting
  implemented ttl
  implemented expireat
  implemented expire
  refactorings, integrating expiration feature into setex, implemented psetex
  implemented set xx
  set px implementation
  expiring keys support
  renamed test method
  setnx implementation complying with test_set_should_accept_nx
  wake up tests: redis 2.7.6 compatibility
  updated tests for TestRealRedis test-case
  updated requirements