modified ignore
Modified builder of DiffRowGenerator to accept custom Equalizer<String> instances to compare lines during diffs
Added null checks.
refs #1: reformat .gitignore
refs #1: Equalizer does not have to care about `ignoreWhiteSpace`.

Now we have 2 classes which has to care about `ignoreWhiteSpace`
and here is 2 bugs:

1. it converts `null` to empty string
2. `Builder.ignoreWhiteSpace` doesn't work when we set custom
   Equalizer

This change solves these problem.
close #1: add <contributor> to pom.xml.
Merge branch 'pr1'
upgrade maven-javadoc-plugin to automate deployment
[maven-release-plugin] prepare release diffutils-1.5.0