Update README.md

Update version information
Rely on checking for PASSWORD_DEFAULT, which should ALWAYS be available.

Since this is supposed to be forward compatible.  What happens if BCRYPT is pulled one day for any reason?  This would break forward compatibility, but relying on PASSWORD_DEFAULT should be safe.

I think another option would be:

if ( ! function_exists('password_hash') ) {
}
Merge pull request #26 from johncongdon/master

Fix for potential forward compatibility break.
updated readme to show a php 5.3 compatible example
Merge pull request #31 from staabm/patch-1

updated readme to show a php 5.3 compatible example
added link to php.net password_* chapter
Merge pull request #32 from staabm/patch-1

added link to php.net password_* chapter
 README: Update reference to the security issue with bcrypt before 5.3.7, for clarity.
Merge pull request #35 from BitLucid/master

 README: Popped in a link to the details of the security issue with bcrypt before 5.3.7...
Fix wrong Base64 encoding (issue #38)
Fix handling of binary and ASCII strings
Prevent warnings from open_basedir
Move binary implementation to separate namespace (to avoid polluting the global namespace with non-core functions)
Add travis build support on HHVM, for better testing
Merge branch 'encoding-fix' of https://github.com/Jacques1/password_compat into Jacques1-encoding-fix
Make tests pass on current 5.5 version, need to find a better way to account for newer builds
Merge pull request #41 from Jacques1/open-basedir-fix

Prevent warnings from open_basedir
Add test to double-check that generated hash is a bcrypt hash. Partially fixes #45
Merge branch 'master' of github.com:ircmaxell/password_compat
Finish HHVM support... At least travis wise