Add support for WordPress plugins

[anderly]

The WordPress plugin repository provides some nice at a glance info that would be useful in badges (plugin version, rating, downloads, supported WP version, etc.) Example: https://wordpress.org/plugins/akismet

Proposed:

---

Plugin Version

/wordpress/plugin/v/<plugin-slug>.svg

---

Plugin Downloads

/wordpress/plugin/dt/<plugin-slug>.svg

(10000+)

(< 10000)

(< 1000)

(< 100)

(0)

---

Plugin Ratings

/wordpress/plugin/r/<plugin-slug>.svg

(4+ stars)

(< 4 stars)

(< 3 stars)

(< 2 stars)

(0 stars)

---

Supported WordPress Version

/wordpress/v/<plugin-slug>.svg

Cross-check a plugin's "Compatible With" value with list of supported WP Versions found here: https://api.wordpress.org/core/version-check/1.7/

(Current: Tested with most current WP version)

(Warn: Not tested with most current, but still in supported list)

(Out of date: Not tested with any versions in supported list)

---

All of this information can be retrieved by making an API request to http://api.wordpress.org/plugins/info/1.0/{slug}.json

Example: http://api.wordpress.org/plugins/info/1.0/akismet.json

More details on WP.org's API here: http://codex.wordpress.org/WordPress.org_API

[espadrine]

This is fixed by #300. Kudos to @anderly!