I'm trying to take a bunch of year columns and unpivot them to a single column.

Input is something like this:

```
Country 1990 1991
Canada    10   20
Scotland 100  200

```

and what I want is something like this:

```
Country Year  Value
Canada   1990    10
Canada   1991    20
Scotland 1990   100
Scotland 1991   200

```

Is there an easy way to do that? I feel like I should be able to do this in one line with pandas but I can't get it.

The real transformation I want to do is even more complex. The above is just one step along the way I think.

The full problem would be like what's below. Can it be done in one step or would I have to do multiple transformations?

```
Country  Measure 1990 1991
Canada   M1        10   20
Canada   M2       0.1  0.2
Scotland M1       100  200
Scotland M2         1    2

```

I need this:

```
Country  Year  M1  M2
Canada   1990  10 0.1
Canada   1991  20 0.2
Scotland 1990 100   1
Scotland 1991 200   2

```

I've tried various combinations of `pivot` and `stack` and it's not what I need.