Strict enforcing of allowed post types

There has been a regression which allows wordpress objects that are not post or page types (notably attachments) to get pushed to Discourse, which this should fix
Extended for loop to cover the list
Replaced deprecated $wpdb->escape 

$wpdb->escape has been deprecated and should be replaced with esc_sql to avoid notice messages in log file. 
https://www.webniraj.com/2013/08/05/wordpress-3-6-fixing-wpdbescape-deprecation-errors/
Merge pull request #58 from wdbetts/patch-1

Replaced deprecated $wpdb->escape
Merge pull request #50 from anthonydillon/master

Extended for loop to cover the list
Merge pull request #32 from surrealroad/patch-7

Strict enforcing of allowed post types
Support pushing an `embed_url` for an article across to discourse
Bump version
Use parse_args to ensure default options are set

When unsetting option values the key was getting removed from
option_value in wp_options, blowing up code that read from $options.
Using wp_parse_args will ensure those missing values get the default.
This only fixes errors in publish_to_discourse, there are other places
where this is still a problem.