Release 0.3.1

BUG FIXES

* Ensure submodules are refreshed for merge conflict detection
  (rschlaikjer, #73, #75)
* Ensure the proper remote is fetched for merge conflict detection
  (rschlaikjer, #74, #75)
* Hard reset and clean pre-checkout to prevent checkout being blocked
  by unstaged changes (rschlaikjer, #76)
* Force delete / recreate of test branches, to fix branches that
  might not have been cleaned up properly (rschlaikjer, #76)

PERFORMANCE TWEAKS

* For performance reasons, only perform a fetch when a new remote or
  pickme has been added (rschlaikjer, #76)