Use HTTPS_PROXY environment variable

The Trello API uses the https protocol, so the gem should
use the https proxy environment variable accordingly.
Merge pull request #48 from onibox/proxy-env-variable

Use HTTPS_PROXY environment variable
Restrict rescue statement to RestClient::Exception

Exception#http_code and Exception#http_body are only provided by
RestClient::Exception, so restrict the rescue statement to those
types of exceptions.
Merge pull request #49 from onibox/catch-restclient-exceptions

Restrict rescue statement to RestClient::Exception
reverts #48
retrieve label names at the board level
added tests for label_names
Merge pull request #50 from set5think/master

adding the ability to retrieve label names at the board level
adding dateLastActivity to card object, useful for tracking changes
changing date_last_activity to be more readable: last_activity_date
Merge pull request #51 from set5think/master

adding dateLastActivity into the card object, a useful field that's available via the trello API
fixes card spec having wrong identifier
add missing fields for an Attachment (url, member_id, date, mime_type, is_upload)
Merge pull request #52 from rcugut/attachment-extra-fields

add missing fields for an Attachment (url, member_id, date, mime_type, i...
Merge branch 'master' of git://github.com/jeremytregunna/ruby-trello
removing trailing spaces in trello.rb