Issue #91 Verify checkstyle rules during the build process

Fixed issues found when running checkstyle:
- Added missing Javadocs
- Added missing package-info.java
- Enabled javadoc style checkstyle rule
Replaced direct uses of AST with ASTBuilder.
Factorized code.
Corrected issues found by FindBugs and Coverity.

Utils.java:
Inlined basicEquals() to help static analyzers do their job.
Fixed copyright dates.
Fixed wrong file header.