Added back functionality to create new author

Added back the functionality to create a new author that was previously
removed for 0.2.1 release.
Options field for multiple authors

Returned options field for multiple authors that was removed for 0.2.1
release.
Callback for multiple authors option field

Added callback function for multiple authors option field that was
removed for 0.2.1 release.
Validation for multiple authors option field

Added back validation check for multiple authors option field that was
removed for 0.2.1 release.
Button for Create New Author

Added button for creating a new author in the meta box that was removed
for 0.2.1 release.
Removed $post input argument

Removed $post input argument as it is not needed by the function and
was throwing an error when creating a new post.
New Author meta box

Added the New Author meta box code that was removed for 0.2.1 release.
Include class for multiple authors

Add call to include multiple authors class that was removed for 0.2.1
release.
Added check for multiple authors enabled

Added conditional for multiple authors that was removed for 0.2.1
release.
Added multiple authors to plugin activation

Added entry for multiple authors option field to plugin activation call
that was removed for 0.2.1 release.
Added changelog entry

Added a changelog entry for the next plugin release (currently expected
to be 0.2.2)
Restored Multiple Author and New Author files

Restored files that were removed for 0.2.1 release.