Consider changing .column to .col

This was briefly discussed in #823. Currently, nalgebra has methods like `.row(i)` and `.column(i)`, and similarly across different functions and types. For symmetry with `row`, it would perhaps be preferable to use the abbreviated (but arguably unambiguous) form `col`. We could deprecate current methods that use the full word `column`.

This would be a good first issue for someone's first contribution, but I'm hesitant to have someone start work on this before I know that there are no (strong) objections.