Add test coverage with Coveralls/slather

.slather.yml

@@ -0,0 +1,3 @@
+coverage_service: coveralls
+xcodeproj: Example/Espressos.xcodeproj
+source_directory: TTTAttributedLabel

.travis.yml

@@ -1,10 +1,13 @@
 osx_image: xcode61
 language: objective-c
-before_install: gem install cocoapods xcpretty -N
+before_install: gem install cocoapods xcpretty slather -N
 cache: cocoapods
 podfile: Example/Podfile
 env:
   - LC_CTYPE=en_US.UTF-8 LANG=en_US.UTF-8
 script:
-  - set -o pipefail && xcodebuild -workspace 'Example/Espressos.xcworkspace' -scheme 'Espressos' -sdk iphonesimulator -destination "platform=iOS Simulator,name=iPhone 6" clean test | xcpretty -c
+  - set -o pipefail && xcodebuild -workspace 'Example/Espressos.xcworkspace' -scheme 'Espressos'
+    -sdk iphonesimulator -destination "platform=iOS Simulator,name=iPhone 6"
+    GCC_INSTRUMENT_PROGRAM_FLOW_ARCS=YES GCC_GENERATE_TEST_COVERAGE_FILES=YES clean test | xcpretty -c
   - pod lib lint --quick
+after_success: slather

README.md

@@ -1,6 +1,6 @@
 # TTTAttributedLabel
 
-[![Build Status](https://travis-ci.org/TTTAttributedLabel/TTTAttributedLabel.svg)](https://travis-ci.org/TTTAttributedLabel/TTTAttributedLabel)
+[![Build Status](https://travis-ci.org/TTTAttributedLabel/TTTAttributedLabel.svg)](https://travis-ci.org/TTTAttributedLabel/TTTAttributedLabel) [![Coverage Status](https://coveralls.io/repos/TTTAttributedLabel/TTTAttributedLabel/badge.svg)](https://coveralls.io/r/TTTAttributedLabel/TTTAttributedLabel)
 
 **A drop-in replacement for `UILabel` that supports attributes, data detectors, links, and more**