Feature request: absolute import support

[bo-ku-ra]

when importing d2-file that define 'style' and 'classes', absolute path is better than relative path.

move "cccc.d2" "./bar/cccc.d2"

├─d2
│ │ bokura-config.d2
│ │
│ └─foo
│ │ aaaaa.d2 (classes{ ...@../bokura-config.classes })
│ │ bbbbb.d2 (classes{ ...@../bokura-config.classes })
│ │ (ccccc.d2) <-OK
│ │
│ └─bar
│ ccccc.d2 (classes{ ...@../bokura-config.classes }) <- NG (../../ <-OK)

[bo-ku-ra]

i may want to put 'bokura-config.d2' on a network drive when i share it with my colleagues.