Add methods to HDTManager store an index at custom place

[jmkeil]

Currently, a index created with HDTManager::doIndexedHDT will automatically be storied to a default path (the working directory). It would be very helpful to provide methods to

• create an index in memory, without writing them to the file system; current workaround:

((TriplesPrivate) hdt.getTriples()).generateIndex(null);

• store a existing index into a provided OutputStream out; current workaround:

((TriplesPrivate) hdt.getTriples()).saveIndex(out, new ControlInformation(), null);

• Load an earlier created index from a provided InputStream in; current workaround:

ControlInformation ci = new ControlInformation();
ci.load(in);
((TriplesPrivate) hdt.getTriples()).loadIndex(in, ci, null);

I think, a user of the library should not need to go that deep into the implementation to do this.

[mielvds]

Hi @jmkeil would you mind opening a PR for this?

[jmkeil]

Hi @jmkeil would you mind opening a PR for this?

As I decided against using HDT in my project, I don't have time to do that. Sorry.