PostsController#show method/specs added.

With a totally bogus view template in `app/views/show.slim` that merely
proves that nothing being done now exercises it. We'll add feature
specs to fix that, next.

RSpec: 524 examples, 0 failures
RuboCop: 132 files inspected, no offenses detected
Added first working PostData :show template.

Next up: proper feature specs. View specs Would Be Very Nice too.

RSpec: 524 examples, 0 failures
RuboCop: 132 files inspected, no offenses detected
Post :show page now displays GFM markup as HTML.

Now ready to start hooking the bare :show action (which works) into the
UI. Pinging Issue #64.

RSpec: 524 examples, 0 failures
RuboCop: 132 files inspected, no offenses detected
[Fix #64] Landing page has links to each post.

Instead of just showing the post title, now shows a link to the post,
using the title as link text.

RSpec: 526 examples, 0 failures
RuboCop: 133 files inspected, no offenses detected
Merge pull request #76 from jdickey/new-issue-64

Fixes Issue #64.