_s: Simplify entry meta output

- Fix entry-footer inconsistency between content-*.php files
- Move in a function <code>_s_entry_meta()</code> to avoid duplication

---

At the moment there is an inconsistency between content.php and
content-single.php regarding the .entry-footer output.

In my opinion content.php output is would be better to use because it's
easier to translate and allow more customisation.

Finally by moving it into <code>inc/template-tags.php</code> we are
getting rid of some duplicated code.
Removed vendor prefixes, except where it fixes a specific bug or quirk
Prepare Underscores for Coding Standards. See https://github.com/Automattic/_s/issues/553.
Update archive.php

Revising the "primary" element to use a "div" vs. "section" to bring it into sync with index.php and single.php
Prepare Underscores for Coding Standards. See https://github.com/Automattic/_s/issues/553. [skip ci]
Merge pull request #581 from philiparthurmoore/master

Introduce Coding Standards Checks into Underscores
Kick off Travis CI Build Monitoring for _s

See https://github.com/Automattic/_s/issues/553.
Changes description of mixin - props @r007

Relates to #582
Rewording "plugin" to "theme"
Merge pull request #586 from yoarts/patch-1

Change plugin references to theme references in Travis CI config file.
Add fixes for faulty Sass @import paths and negative values.
Change Sass headings file name and import path.
Merge pull request #596 from MickeyKay/sass-header-file

Change Sass headings file name and import path.
Merge pull request #594 from MickeyKay/sass-fixes

Add fixes for faulty Sass import paths and negative values.
Closes #588.
Update style.css

fixes #587
Delete hyphens

in comment headings
Merge pull request #601 from pixelstrolch/comments-hyphens

Delete hyphens.
_s: Update to entry meta output. See #537

* Rename function
* Move edit link outside of function
* Remove comments link on single post
Add hidden post title to the continue reading link
Merge pull request #516 from chrisdc/continue_reading_link

Add post title to the continue reading link for context.