Merge pull request coinbase#20 from coinbase/swift_2_3_and_extensions

Swift 3 and extensions

Merge pull request coinbase#19 from coinbase/update-version

Increment version 3.2.6

Merge pull request coinbase#42 from coinbase/user-agent

User agent

Bumped to 3.2.4

Bumped to 3.2.3

Merge pull request coinbase#39 from coinbase/timeout-variable

Added request TimeoutInterval variable.

Bumped to 3.2.1

Bumped minimum supported iOS platform to 8.0

Fix bug where forKey: was being used instead of forHTTPHeaderField:

Merge branch 'master' of github.com:coinbase/coinbase-ios-sdk