Feature Request: Ability to disable the auto sizing of panes

[tjones-ieee]

Hello,

I really appreciate splitpanes - it's been a great tool for a neat look and feel for my app.

I would like to request a new feature to disable the automatic sizing of panes when a new pane is added. The use case would be programmatically adding panes when the size of all panes is strictly controlled. For example:

const panes = [
  {
    id: 1,
    size: 50,
  },
  {
    id: 2,
    size: 50,
  },
]

// wait for some use action to "add a new pane"
panes.push({
  id: 3,
  size: 25,
});
panes[1].size = 25;

Current behavior for this use case results in pane sizes of 37.5, 37.5, and 25, respectively.
Expected behavior with a way to disable the auto sizing would be pane sizes of 50, 25, and 25.

This may cause some internal splitpanes calculation issues, so perhaps set a delay when panes are added to verify their total size is equal to 100, and if not perform the auto size.

Thanks,
Tyler