Add ability to start from user specified hash.

This feature can be useful for repositories with already established versioning, but
having hundreds of commits which could potentially produce really weird results due
to lack of previous rules on wording.

config.yaml

@@ -1,6 +1,7 @@
 version: 1
 force:
   major: 1
+  # commit: 69fbe2df696f40281b9104ff073d26186cde1024
 wording:
   patch:
     - update