commoncrypto PBKDF2 support
update commoncrypto pbkdf2 with new naming
update changelog
Merge branch 'master' into pbkdf2-commoncrypto

* master:
  a bit more language work + changelog changes for pbkdf2hmac
  one more style fix
  a few typo fixes, capitalization, etc
  switch to private attributes in pbkdf2hmac
  expand docs to talk more about the purposes of KDFs
  update docs re: PBKDF2HMAC iterations
  add test for null char replacement
  Added installation section to index.rst
  called -> used
  quotes inside, diff examples
  Expose this method because probably someone will need it eventually
  fix spacing, remove versionadded since HashAlgorithm was in 0.1
  document HashAlgorithm
  Added canonical installation document with details about various platforms, fixes #519
  update docs for pbkdf2
  Add bindings for X509_REQ_get_extensions.
  add Konstantinos Koukopoulos to AUTHORS.rst
  review fixes
  doc updates based on review

Conflicts:
	docs/changelog.rst
simplify check for algorithm
Merge pull request #531 from reaperhulk/pbkdf2-commoncrypto

PBKDF2HMAC (CommonCrypto)