In order to realistically test rosbagmigration, we had to create
several generations of messages which mutate and migrate and generate
bag files across all of them.

At each generation, we generate a bagfile with the contents of all of
the messages and the corresponding migration rules to migrate the
previous generation forward.

To use a particular generation script, move msgs_N to msgs, and then
run script/generate_data_N.py.  The bash script "generate_data" does
this for all generations.  The helper scripts, "gen1, gen2, gen3, gen4,
and current" switch the message context to that particular


GENERATION 1:
 Unmigrated.msg
 Subunmigrated.msg
 PartiallyMigrated.msg
 MigratedExplicit.msg
 MigratedImplicit.msg
 MigratedMixed.msg
 Renamed1.msg
 Convergent.msg
 Converged.msg
 Hierarchical.msg
 SuperHierarchical.msg


GENERATION 2:
 Unmigrated.msg
 Subunmigrated.msg
 PartiallyMigrated.msg - implicit
 MigratedExplicit.msg  - explicit
 MigratedImplicit.msg  - implicit
 MigratedMixed.msg     - implicit
 Converged.msg         - Rename from Convergent.msg
 Renamed2.msg          - Rename from Renamed1.msg
 Hierarchical.msg
 SuperHierarchical.msg

GENERATION 3
 Unmigrated.msg
 Subunmigrated.msg
 PartiallyMigrated.msg - explicit
 MigratedExplicit.msg  - explicit
 MigratedImplicit.msg  - implicit
 MigratedMixed.msg     - explicit
 Converged.msg         - explicit
 Renamed3.msg          - rename from Renamed2.msg and explicit
 Hierarchical.msg      - explicit
 SuperHierarchical.msg - implicit

GENERATION 4:
 UnMigrated.msg        - explicit  (No corresponding rule)
 Subunmigrated.msg
 PartiallyMigrated.msg - explicit  (No corresponding rule)
 MigratedExplicit.msg  - explicit
 MigratedImplicit.msg  - implicit
 MigratedMixed.msg     - implicit
 Converged.msg         - implicit
 Renamed4.msg          - rename from Renamed3.msg
 Hierarchical.msg      - implicit
 SuperHierarchical.msg

CURRENT:
 UnMigrated.msg        - explicit  (No corresponding rule)
 Subunmigrated.msg
 PartiallyMigrated.msg - explicit  (No corresponding rule)
 MigratedExplicit.msg  - explicit
 MigratedImplicit.msg  - implicit
 MigratedMixed.msg     - implicit
 Converged.msg         - implicit
 Renamed5.msg          - rename from Renamed4.msg
 Hierarchical.msg      - implicit
 SuperHierarchical.msg


