Add error handling for gateway timeout errors

#503
#502
Thanks to @adsteel

Fix regression in Request class

Fixes a regression introduced in 3.9.2 which privatised an attribute accessed outside of the Request class.

#499

Handle unexpected response bodies

#492 @adsteel

Handle unexpected response bodies and raise appropriately.

3.9.1 was skipped due to a bug in the release mechanism.

Add Teams endpoint

Add support for teams endpoint
#488

Add error handling for company not found

Adds automatic handling for the company_not_found error
#485

Add support for Customer Search API

Add support for Customer Search (currently in Unstable API Version)
https://developers.intercom.com/intercom-api-reference/v0/reference#customers

Remove deprecated Rubyforge reference

#477

Add InvalidDocumentError handling

Handle invalid document errors more thoroughly.
#465

Added error handling for scroll exists error

Added error handling for scroll_exists error.

#462

Added API versioning support

You can now specify the version of Intercom's API that you would like to use.

intercom = Intercom::Client.new(token: "my_token", api_version: "1.0")

#459