Only build carthage scheme for CI by default

It encompasses CarthageKit and its tests already, so no need to build
everything.
Add .travis.yml
Work around Xcode beta Optional incompatibility
Notify Slack, not email
No travis emails, please
Regenerate Slack key with encryption
Merge branch 'master' into travis-ci
Add KEY_PASSWORD envvar for codesigning
Add encrypted iOS development certificate
Create a temporary keychain on Travis for signing
Verbosify
Fix verbose `security` invocations
Stop using `security` verbosely, actually
Make the temporary keychain the default
Merge branch 'fix-task-output-race' into travis-ci
Suppress xcodebuild output from tests

Travis doesn’t like > 4 MB log files, soooo…
Suppress fixture-copying output too
Merge pull request #130 from Carthage/travis-ci

Set up Travis CI