Update cb4j-core/src/main/java/net/benas/cb4j/core/validator/RegExpFieldValidator.java

Update RegExpFieldValidator to use String.matches as validator 
Update cb4j-core/src/main/java/net/benas/cb4j/core/validator/NumericFieldValidator.java

NumericFieldValidator is a regular expression validator so let's extend this class from RegExpFieldValidator
Update cb4j-core/src/main/java/net/benas/cb4j/core/validator/EmailFieldValidator.java

EmailFieldValidator is a regular expression validator so let's extend from RegExpFieldValidator
Merge pull request #4 from nihed/master

Merge pull request #4 from nihed : Regular Expression Review