Nested Takefiles

[luvies]

add the ability to load in a secondary Takefile (with any name) into a target as its children, allowing Takefiles to be composed of one-another. example:

{
  target1: {
    imports: 'take/imports1.ts'
  },
  target2: {
    imports: [
      'take/imports2.ts',
      'take/imports3.ts'
    ],
    children: {
      child1: {...},
      child2: {...}
    }
  }
}

the children will be merged together (throwing errors if any top-level targets from any of the imported Takefiles clash with the children, or each other), and a Takefile can be imported multiple times (just not in the same target). the top-level imports of the imported Takefiles can also specify depParent: true to depend on the target that imports them (thus, importing a Takefile multiple times can affect how it runs).