Fixes #17
Merge branch 'release/1.6.1'
Update README.md
Merge pull request #18 from throrin19/master

Flattr Button
Merge pull request #19 from throrin19/development

Flattr Button
Updating android-maven-plugin to version 3.8.0.
Merge pull request #21 from paddyzab/master

Updating android-maven-plugin to version 3.8.0.
Merge branch 'release/1.6.2'
Remove unnecessary comments.
Refactoring of the class.
Refactoring of the validator (too much boilerplate code).
Change base class name to be more elegant.
Refactor validate. Make base classes more abstract.
Change expressions with iterator to enhanced for-loop.
Refactor class. Change variables names to be more consistent.
This class makes no sense.
Update build.gradle with current versions.
Update build.gradle to support robolectric tests.
Conigure Robolectric to support eclipse project structure.
Create tests for all numbers validator.