enhancements for idea.sh shell script

The -o option of the idea.sh shell script is almost impossible use and should be renamed (since it is used only for testing). First, the operand is relative to the top of the repo. containing the current directory, so it must almost certainly be a simple pathname. Second, it must have a final path component "idea." if the IDE is to recognize it. These factors mean you can only say "idea.sh -o .idea" to get meaningful results. A real -o flag would place the result relative to the script caller's current directory, and would ensure that the final result had the needed ".idea" component.

Given those improvements to the -o flag it might be possible to set up several IDE projects in one repo. This would be helpful to some programmers especially in repos with many branches, although others will continue to make one repo per active branch.

It should be possible to name packages within modules, asking the script to generate subsetted projects that operate only on the given folders. Currently, using Intellij on the "java.base", which has about 3k source files, is difficult because of the long pauses when the IDE must rescan the source and class files for java.base. But if I'm working only in (say) java.lang and java.lang.invoke (about 175 sources), I should be able to get a configuration that looks only at those files.

It would be helpful if the idea.sh file could dump a few hints, or at least a URL, telling me what are my next steps after I have generated the IDE project.

All of these suggestions have alternative workarounds: Use the existing script and then manually fix the results. That's OK for experienced users. But the idea.sh script should also help novices to get started looking at the sources.