Row and column slice getter

[ibarrond]

Adds get_row and get_col functions to access the corresponding underlying slice of a selected row/column, returning None if out of bounds or if the values are not contiguous (e.g., a row from a grid in Order::ColumnMajor or a column from a grid in Order::RowMajor).

Equivalent mutable methods get_mut_row and get_mut_col.

EXTRA: some quick linter fixes.

[ibarrond]

@becheran Any chance this can be merged sometime soon?

[becheran]

First of all thanks for openening a PR.

I don't understand why those additional function whould make the library more useful? Especially because all function only work properly in one of the two modes.

[becheran]

I had a look at the changes. Thanks for the formatting. I better setup my auto-formatter better.

I wonder if the implementaiton helps or is more confusing. I don't think it is a good idea to expose a function called get_row which only works in RowMajor mode.

Why not use the already existing iter_row funciton instead and let the caller decide if collecting the result into a Vec is desired?