add a few missing entries to CHANGES.rst
add a few missing entries to CHANGES.rst

This adds four notes to the changelog for:

 - Issue #125 (mysqldump estimation failures under MariaDB 10.1)
 - Issue #121 (hook commands are no longer run under --dry-run)
 - Issue #116 (pgdump now escapes passwords for PGPASSFILE)
 - PR #95 (gpg added as a compression target)

m00dawg/holland,m00dawg/holland