Update docsprint to reflect the new xapian-letor.

[AyushP123]

I have updated the docsprint to account for changes in xapian-letor.

[jaylett]

As I mentioned on IRC, this cannot maintain the structure of the documentation file from xapian-letor. I believe it needs to have a very brief introduction into what letor actually does (it reorders a match set to bring more relevant documents to the top, using a more sophisticated approach to calculating relevance than probabilistic weighting schemes like BM25), then show how to use it. Finally, at the end, it can talk about the background in more detail; but you don't have to understand it in order to use letor.

You should look at the rest of the repo to see how examples are done. They should be complete programs, out of which specific line ranges are included in the documentation. You'll have to write the examples in C++ (because language bindings aren't available for letor yet). The way this is done will also provide syntax highlighting for the code snippets.

And you must build documentation and look at it before opening a pull request. This PR has a number of RST syntax errors and incorrect uses which are obvious as soon as you look at the rendered output. This is the documentation equivalent of tidying up C++ source code: it must build without errors, and it should follow the conventions already established in the rest of the documentation, as far as possible.

A final note: all the stuff about extendability should be removed. As it stands, it's either obvious (to add a new Scorer, you subclass Scorer) or incorrect (users of Xapian don't have to put new scorers into the Xapian build tree, and indeed should not). Once we have basic documentation in place we can perhaps think of a way of explaining with a practical example how to extend letor.

I suggest you make the relevant changes then force push a new commit, and then add a comment here to indicate that it's ready for review; right now there are enough issues you can pick up yourself from the above without it being worth pointing every single one out, and given the need to restructure the document, I think fixup commits are going to be hard to follow.

[AyushP123]

I have published the c++ documentation online here. Learning to Rank is published here. We can use this site to provide c++ documentation along with the default python documentation that we have.

[ojwb]

Thanks for the update - a few minor things:

[AyushP123]

Hi,
I am very sorry for the late fixup. There are more issues present in the documentation which need to be ironed out. I remember addy getting confused on a lot of topics. Will go through them again and create a new PR.

[VaibhavKansagara]

@AyushP123 let me know if I can help with any of those issues. Also what do you think about adding documentation of xapian-letor-update in the main repository?.

[ojwb]

Will go through them again and create a new PR.

I'd suggest it's probably worth addressing the last few issues here first so we can merge this first as it's already a significant improvement over the current situation.

Then a new PR can build on that.

[ojwb]

This change is wrong - it's only the --db= part which isn't expected - the DBPATH part is.

[ojwb]

Putting spaces after the commas in code would better match the other code examples.