Added equalToWithDiff for comparing strings with diff message

[night-gale]

Fixed #209 Added a new Matcher equalToWithDiff for compare string. When mismatch happens, instead of output two strings, only lines that mismatch would be output. For words in those lines that mismatch would be surrounded by ~, the expected words would be surrounded by **.

• To implement this, the external library io.github.java-diff-utils:java-diff-utils:4.5 is introduced.
• test class IsEqualWithDiffTest is created

[night-gale]

The library io.github.java-diff-utils:java-diff-utils:4.5 uses some java 1.8 features. That could be the reason why only the compilation with java 1.7 fails. Maybe issue #331 should be resolved first...

[nhojpatrick]

Going to try and kick start hamcrest, so if you want to get it merged, please rebase from the branch v2.3-candidates. Still trying to understand how has permissions to perform a release.