Adopt matrices/2d-arrays in the classic API

[PMeira]

Although some of the current code already handles the dimensions, there are more functions that return 2-d arrays that are not handled.

The C-API, both for the native AltDSS and our Oddie wrapper for EPRI's OpenDSS distro, includes the dimensions in 26 or so functions. Since we just need to use the info provided by the library directly, it's a simple update. It will simplify the existing 2d arrays code too.

This is a breaking change, so it could be done in a dedicated release. The next release (v0.10.0) already includes too many other changes, most of them non-breaking.