Tabmat

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**Bug fixes:**

- Handling for nulls when setting up a ``CategoricalMatrix``
- Fixes to make several functions work with both row and col restrictions and out

**Other changes:**

- Added various tests and documentation improvements

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**Breaking change:**

- Rename `dot` to `matvec`. Our `dot` function supports matrix-vector multiplication for every subclass, but only supports matrix-matrix multiplication for some. We therefore rename it to `matvec` in line with other libraries.

**Bug fix:**

- Fix a bug in `matvec` for categorical components when the number of categories exceeds the number of rows.

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See git history.