Redo `[variables]`

[mrexodia]

Currently specifying cache variables is a huge pain. The use case is variables that need to be set before the project call:

set(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "")
set(CMAKE_BUILD_TYPE "Release" CACHE STRING "")

project(x)

[variables]
CMAKE_BUILD_TYPE = { cache = "Release" }
CMAKE_CONFIGURATION_TYPES = { cache = "Debug;Release" }

[project]
name = "x"