Move Enumeration sources into Maven dir structure

Maven is so happy now.

src/cpp -> src/main/cpp
src/Csharp -> src/main/Csharp
src/edu -> src/main/java/edu

test/cpp -> src/test/cpp
test/Csharp -> src/test/Csharp
test/edu -> src/test/java/edu
Move open-dis sources into Maven dir structure

src/main/edu -> src/main/java/edu
src/test/edu -> src/test/java/edu
Add maven-gpg-plugin for signing artifacts

Artifacts must be signed to be deployed to Maven Central to prove
authenticity.

$ mvn release:perform
gitignore ant build dirs
Fix typo in Maven scm connection URL
Specifiy the Java source and target versions in the pom.xml's

Using what was previously declared in the build.xml files:

sedris -> 1.5 (wasn't specified, but is the javac default)
Enumerations -> 1.5
open-dis -> 1.6