Do not return nil pointers when loading ignores (fixes #846)

Not sure, perhaps we should check for error, and respect that instead.
But then in the walker we'll have to check for a nil pointer anyway.
Merge pull request #850 from AudriusButkevicius/nil

Do not return nil pointers when loading ignores (fixes #846)
`-generate` flag should also create config.xml (closes #847).
Fix a missed nil (fixes #846)
Revert and replace 31d95ac, 65acc7c, 87780a5
Keep temporaries for reuse, cleanup before pull (fixes #849, fixes #841)
Add Nutomic
Merge remote-tracking branch 'origin/pr/852'

* origin/pr/852:
  `-generate` flag should also create config.xml (closes #847).
Merge pull request #853 from AudriusButkevicius/unfinished

Keep temporaries for reuse, cleanup before pull (fixes #849, fixes #841)
Merge pull request #854 from AudriusButkevicius/nils

Revert and replace 31d95ac, 65acc7c, 87780a5
Implement BlockMap
Populate BlockMap
Implement block fetcher (fixes #781, fixes #3)
Fix tests
Track total block counts, count copier blocks

Will eventually allow us to track progress per file
Add fetcher tests
Delete files and directories after pulling