fix pre-version enforcement
Merge pull request #40 from julienledem/fix_preversion_enforcement

fix pre-version enforcement
[maven-release-plugin] prepare release 0.9.27
[maven-release-plugin] prepare for next development iteration
Fix #41: abstract could become concrete.
Merge pull request #42 from mschonaker/master

Fix #41: abstract could become concrete.
[maven-release-plugin] prepare release 0.9.28
[maven-release-plugin] prepare for next development iteration
[maven-release-plugin] prepare release 0.9.29
[maven-release-plugin] prepare for next development iteration
Update README.md
Fix jardiff's Tools.isAccessChange(..): Differentiate between Class, Field and Method and apply all rules of the Java Language Specification

Class, Field and Methods have different binary backward compatibility rules
as specified in the Java Language Specification, Java SE 7 Edition:
  - http://docs.oracle.com/javase/specs/jls/se7/html/jls-13.html

For Field 'volatile' the Java Language Specification, first edition has been used:
  - http://www.wsu.edu/UNIX_Systems/java/langspec-1.0/13.doc.html#45194

For each type separate method have been created, i.e. Tools.is<Type>AccessChange().
Each new method has the rules referenced and partially copied into the method
for better documentation.

The now deprecated method Tools.isAccessChange(..) calls Tools.isClassAccessChange(..)
and shall be removed.

Unit test ToolsTest has been expanded for each type and its rules.