Issue #3: Adds compatibility with PHP versions prior to 5.3.3
Updated a bug where attachments were not actually uploading their content
Update Users.php

Fix create_many endpoint using "user" key bug
Update Http.php

When $json is a string, the condition on line 48 is evaluated like so :
isset($json['filename'])
-> isset($json[0])  (string when interpreted as a integer becomes 0)
-> isset({first character of $json})

And so fopen then attempts to open a file named '{'.
Merge pull request #20 from rene-lafleur/patch-1

Update Http.php
Merge pull request #18 from d-ph/master

Fix small bug in Users.php
Merge pull request #17 from rohjay/bugfix-attachment-content

[bugfix] Attachment content not uploading
Merge pull request #11 from joeelizondo/compatibility_fix

Issue #3: Adds compatibility with PHP versions prior to 5.3.3