This allows users to "map" (or "link") symbols with different names so that they can be compared without having to update either the target or base objects. Symbol mappings are persisted in objdiff.json, so generators will need to ensure that they're preserved when updating. (Example: d1334bb79e)
Resolves#117
Job status is now shown in the top menu bar,
with a new Jobs window that can be toggled.
Build and diff errors are now handled more
gracefully.
Fixes#40
