Prepare release v0.1.2

Changes since v0.1.1
- Accept qualified (remote) branch names (that is
  'remotes/origin/branch' instead of 'origin/branch').
- v0.1.1 introduced a bug, that resulted in push-merges not being
  considered when calculating the merge base (more precise: they have
  been considered only if "my-prefix" was equal to "their-prefix"). This
  issue is now resolved.
- When parsing their branch's history, the order of the marker arguments
  is not relevant any more. This might improve forward compatibility.

CHANGELOG

@@ -1,4 +1,4 @@
-# v0.1.2 (SNAPSHOT)
+# v0.1.2 (2016-12-18)
 - Accept qualified (remote) branch names (that is 'remotes/origin/branch'
   instead of 'origin/branch').
 - v0.1.1 introduced a bug, that resulted in push-merges not being considered