Upgrade to BaseX 9

[pralitp]

Upgrade to BaseX 9 and switch to it's new xquery serialization format meant to deal with serializing/parsing large CSV datasets.

This may help with #44.

[pralitp]

TODO: we should update the model interface submodule as well at the very least. I'm not sure if we want to wait to merge until we merge the BaseX 9 changes into master on the modelinteface repo AND I don't know if we want to propose to do this in GCAM yet.

[codecov]

Codecov Report

Merging #47 into master will not change coverage.
The diff coverage is 100%.

Impacted Files	Coverage Δ
R/querymi.R	83.84% <100%> (ø)	⬆️

[rplzzz]

I guess the answer to that depends on whether the baseX-9 changes are backward compatible. Here's what we need to consider:

1. After the merge, will we still be able to read old GCAM output files written with baseX-8?
2. Once GCAM is updated to baseX-9, will the baseX-8 version of rgcam still be able to read its outputs?

If the answer to both of these is yes, then we should increment the patch level of rgcam and go ahead with the merge.

If the answer to 1 is yes, but 2 is no, then we can still go ahead with the merge, but we should increment the minor version of rgcam.

If the answer to 1 is no, then we should increment the major version of rgcam and wait to merge until the corresponding merge goes into GCAM.

[pralitp]

It looks like the answer to 1 is yes and 2 is no.

It sounds like we would be ok with having rgcam proceed with BaseX 9 ahead of GCAM in which case I will proceed by pointing the modelinteface submodule the branch on that repo.