Versioning system

[iammadab]

We should output the field tracker version number as part of the report.

This is so that benchmarks made with a version of field tracker are not compared with benchmarks made with a different version of field tracker (or at least some changelog is made available to see the implications of direct comparison).

Version change could be as a result of:

• tracking new variables
• discovering that some previously tracked metric was not fully tracked
• e.t.c.