Add Balanced Payments API

Summary: Adds the Balanced PHP API to externals/. Ref T2787.

Test Plan: Used in next diff.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran, aurelijus

Maniphest Tasks: T2787

Differential Revision: https://secure.phabricator.com/D5764

Author: epriestley

externals/balanced-php/.gitignore

@@ -0,0 +1,14 @@
+# composer
+.buildpath
+composer.lock
+composer.phar
+vendor
+*~
+*#
+# phar
+*.phar
+
+# eclipse-pdt
+.settings
+.project
+*.iml

externals/balanced-php/.travis.yml

@@ -0,0 +1,8 @@
+language: php
+before_script:
+  - curl -s http://getcomposer.org/installer | php
+  - php composer.phar install
+script: phpunit --bootstrap vendor/autoload.php --exclude-group suite tests/
+php:
+  - 5.3
+  - 5.4