Changelog for 3.0
Targetting 3.0.0

With so many fatures baked into this release, I think now is a good time
to bump the major version number.

Some major things off the top of my head:

* Hack - hacklang.org
* Removing libevent server
* Switching from hdf to ini
* mysqli
* Moved many functions to \HH namespace
* error message format change
* ... many more once I write the blog post
still read config.hdf

Summary: @aatch pointed out that since everything isn't ported he wants a default config still.

Test Plan:
Made a `/etc/hhvm/config.hdf` with

    DynamicExtensions {
      * = pgsql.so
    }

and saw `Uncaught exception: Could not open extension ./pgsql.so: Your system does not support dlopen()`

Reviewers: fredemmott, sgolemon

CC: dmitrys, smith, ps, hphp-diffs@lists

Differential Revision: https://phabricator.fb.com/D1242801
bump version to 3.0.0