Added changelog command to show the changelog since initial commit, last tag or a given range
feature #2 Added changelog command (peterrehm)

Discussion
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Added the changelog command to show the changelog information:

Usage:

php
./gh changelog
Changelog since initial commit:
* feature #1 Added sha2pr command to show merge commit information (peterrehm)

php
./gh changelog --range=d014ad0..HEAD
Changelog for reference range d014ad0..HEAD:
* feature #1 Added sha2pr command to show merge commit information (peterrehm)

Tickets:
- none

Commits
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- 9405cee Added changelog command to show the changelog since initial commit, last tag or a given range (peterrehm)