Release 3.2

[prmr]

• [x] Improve the docs
• [x] Make sure all other issues for the milestone are closed;
• [x] Run all the unit tests;
• [x] Increment the version number in JetUML.java;
• [x] Update the copyrights using the copyright tool;
• [x] Create a new release;
• [x] Write the release notes;
• [x] Release the application on GitHub;
• [x] Create a thin jar that only includes the source code (excluding tests) and the license;
• [x] Package the application as above for the three different platforms;
• [x] Upload the binaries to the release page;
• [x] Close the milestone;
• [x] Tweet about the new release.