Indent code with tabs, not spaces, per WP standards.

This was mostly done except a few lines where spaces had crept in :)

https://make.wordpress.org/core/handbook/coding-standards/php/#indentati
on
Correct indentation to improve readability
Add visibility property to constructor method

This doesn’t change anything but since you’ve used `public` on the
`wp_biblelink_shortcode` method, let’s go ahead and make this
consistent.
Update IF brackets to meet WP code standards

https://make.wordpress.org/core/handbook/coding-standards/php/#brace-sty
le
Make space styles consistent and to meet WP code standards

https://make.wordpress.org/core/handbook/coding-standards/php/#space-usa
ge
Use single quotes when not evaluating anything in the string.

See
https://make.wordpress.org/core/handbook/coding-standards/php/#single-an
d-double-quotes
Merge pull request #3 from paulgibbs/codereview

Code standards review