Revert "Update bundled Gems"

This reverts commit 795df0eabe33d5cec7c2928931703cd8302b8207.

It turns out that this isn't ready for master as the new version of the
mime-types gem requires ruby >= 1.9.2.
Add .md extension to README

So that it looks pretty on GitHub.
Indent code snippets
Update heading style

This is purely my personal preference.
Add notes for week 283.
Add placeholder for week 284 links.
Update version of ratom and libxml-ruby

I ran `bundle update ratom` to get a newer version of libxml-ruby
(2.6.0 up from 2.3.2) as I couldn't get 2.3.2 to compile on my Mac:

    ruby_xml_node.c: In function ‘rxml_node_to_s’:
    ruby_xml_node.c:622: error: dereferencing pointer to incomplete type
    ruby_xml_node.c:624: error: dereferencing pointer to incomplete type
    make: *** [ruby_xml_node.o] Error 1

    make failed, exit code 2

This is similar to [commit 26dc19 in vanilla-rb][26dc19].

[26dc19]: https://github.com/lazyatom/vanilla-rb/commit/26dc1936c3c7f238a06168517a0a9475d51e7ec2
Add a draft of our credit union day 1 post
Tweaks to Project Credit Union - Day 1
Prepare to publish Project Credit Union - Day 1.
Add notes about credit union day 2
More notes for day 2
Add some links for week 284 links.
Added another link for week 284 links.
Add my links for week 284
Tweaks to week 284 links - preparing for publication.
WIP: Project Credit Union - Day 2
Update project-credit-union-day-2.snip.markdown

Add my notes about signing up for London Capital Credit Union.
More changes to Project Credit Union - Day 2.
Add credit union notes for day 3