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.

README.md

@@ -92,6 +92,7 @@ force:
   major: 1
   minor: 0
   patch: 1
+  commit: 69fbe2df696f40281b9104ff073d26186cde1024
 wording:
   patch:
     - update
@@ -107,6 +108,7 @@ wording:
 
 * version: is not respected at the moment, introduced for potential backwards compatibility in future
 * force: sets the "starting" version, you don't need to specify this section as the default is always `0`
+* force.commit allows you to set commit hash from which the calculations should start
 * wording: words the program should look for in the git commits to increment (patch|minor|major)
 
 ### Good to know