_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
Update archive.php

Revising the "primary" element to use a "div" vs. "section" to bring it into sync with index.php and single.php
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.
Inherit box-sizing for best practice

Using inheritance allows easy override on other elements, and also it’s the best practice.
Double quotes for consistency 

```_s``` uses ```""``` throughout except in clearings.
_s: Move edit link in template tag for consistency

Every time `_s_entry_footer()` is used, it’s followed by
`edit_post_link()`. Might as well just move that back in the template
tag.
_s: Update pot file to reflect changes.
Merge branch 'Entry-Meta-Output' of https://github.com/Automattic/_s into Entry-Meta-Output

Conflicts:
	content-single.php
Merge branch 'Entry-Meta-Output'
Merge pull request #612 from emiluzelac/patch-33

Double quotes for consistency.
Remove border-radius mixin
Fix child menu styling inheritance. See #587
Merge pull request #605 from 1upon0/master

Update style.css fixes #587
Update links to those relevant to themes