Default to post author if post editor is missing

Fixes #100
Use customizable deleted-user structure
Enforce string value for display_name
Add missing ')'

Staged only part of a change -- stupid mistake.
Deleted-user variable is not risky
Merge branch 'master' into issue-100
Merge branch 'master' into issue-100
Move buttons to sx-button.el

Also define command to copy button's content under w.
Fix button-map
Improve button-copy
Merge branch 'master' into issue-100

Conflicts:
	sx-question-mode.el
Normalize and improve button help-echo's
New sx--shorten-url function in sx.el
Better help-echo in links
New "Add a Comment" button
Slight tweak to question-mode-recenter-line

So the "add comment" button is visible after navigating to the comments
section.
Woops. Fix swallowing one function inside the other.
Add sx--unindent-text function

Used to extract the code contained in code-blocks
Code-blocks are buttons. RET to edit, w to copy.
Comments