Clean up.
Add `FileSystemStackTask` and `Shared\CommandStack`.
Add `FileSystem::taskFileSystem`.
Fix idiotic typo.
Clean up.
Mod to use `DynamicConfig`, `ExecStackTask` extend `CommandStack`.
Update `FileSystem` to use new `CommandStack` API.
Fix cases with executable.
Refactor `GitStackTask` to use `CommandStack`, same API.
Merge pull request #21 from jadb/0.4-filesystem

Add `FileSystemStackTask` and `Shared\CommandStack`.