Add Travis CI.

Adapted from AppAuth iOS's config (https://github.com/openid/AppAuth-iOS/blob/master/.travis.yml)

.travis.yml

@@ -0,0 +1,23 @@
+# Travis CI config for AppAuth
+# Use the `wwtd` gem to test locally.
+language: objective-c
+osx_image: xcode9
+# Tests iOS, macOS and tvOS: both static library and framework schemes.
+env: 
+# To generate this list, use `xcodebuild -showsdks` to get possible SDK values, and platforms.
+# Use `instruments -s devices` to get the device name.
+  - SCHEME=OpenLocationCode_iOS DESTINATION="'platform=iOS Simulator,name=iPhone 6,OS=11.0'" SDK=iphonesimulator11.0
+  - SCHEME=OpenLocationCode_macOS DESTINATION="'platform=macOS,arch=x86_64'" SDK=macosx10.13
+  - SCHEME=OpenLocationCode_tvOS DESTINATION="'platform=tvOS Simulator,name=Apple TV,OS=11.0'" SDK=appletvsimulator11.0
+before_script:
+  - sudo gem install xcpretty
+script:
+# Breaking down this command:
+# eval is used here, otherwise environment variables are not present.
+# `set -o pipefail && ` is so that the return code isn't gobbled by xcpretty (per https://github.com/supermarin/xcpretty#usage)
+# then it's standard xcodebuild | xcpretty.
+- eval "set -o pipefail && xcodebuild -project OpenLocationCode.xcodeproj -scheme $SCHEME -sdk $SDK -destination $DESTINATION -enableCodeCoverage YES GCC_INSTRUMENT_PROGRAM_FLOW_ARCS=YES GCC_GENERATE_TEST_COVERAGE_FILES=YES OTHERCFLAGS='-Werror' test | xcpretty"
+- eval "swift --version; swift test"
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+

README.md

@@ -1,4 +1,5 @@
 # Open Location Code for Swift
+[![Build Status](https://travis-ci.org/google/open-location-code-swift.svg?branch=master)](https://travis-ci.org/google/open-location-code-swift)
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
 
 Convert between decimal degree coordinates and Open Location Codes. Shorten