No obvious way to concatenate vectors and matricies

When using a dynamic matrix, there is no clear way to extend a matrix not with copies of a _single element_, but with a _vector_ (like with `insert_row` or `insert_column`) or with a _matrix_ (counterpart to `insert_rows` or `insert_columns`). In fact judging by the names, I thought that they used a vector and matrix respectively and not a single value.

This isn't mentioned at all in the reference and I haven't found anything in the API. Is there any reason that concatenation isn't supported when `insert_row` and `insert_column` exist? My current solution is to create a `vec` of vectors and use the `from_columns` constructor.