Version bump to 2.3.0

Bumped version up to match changes in MarkupBlog
Match MarkupBlog author url/link changes

Updated demo files to match the changes to Blog Authors' pages
URL/links.
Updated changelog & instructions

Updated changelog and instructions to reflect changes in MarkupBlog,
especially Blog Authors' pages URL/links.
Various changes, mainly to do with author url/links

- rendersPosts() now uses pageName sanitized author display names
(titles) rather than their usernames in Blog author pages url/links. If
title not set, displays generic 'Author Name' for post author.
- Similar changes to postAuthor() and renderAuthors().
- renderNextPrevPosts() now getting by $post->id rather than
$post->blog_date to cater for multiple posts created via API at same
time (same timestamp).
- Version bump to 2.3.0