replace versioneer with setuptools_scm

[RonnyPfannschmidt]

No description provided.

[codecov-io]

Current coverage is 85.12%

Merging #161 into master will decrease coverage by -0.01% as of 8d330a6

@@            master    #161   diff @@
======================================
  Files           29      29       
  Stmts         5159    5154     -5
  Branches         0       0       
  Methods          0       0       
======================================
- Hit           4392    4387     -5
  Partial          0       0       
  Missed         767     767       

Review entire Coverage Diff as of 8d330a6

---

Uncovered Suggestions

1. +0.81% via borg/fuse.py#124...165
2. +0.66% via borg/xattr.py#199...232
3. +0.56% via borg/xattr.py#166...194
4. See 7 more...

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