Fixup use of undefined variable.
Set charset for new tables to utf8mb4. (Issue #7)
Exit if unable to use utf8mb4 charset. (Issue #7)
Use case insensitive collation on user.name also. (Issue #7)
Migrate tables to utf8mb4. (Fixes #7)
Include mentions table in collation migration.
Convert users table collation as well as columns.

Prevents migration running more than once.
Fixup use of additional users array.
Adjust format of migration output for clarity.
Print message when an exception is caught.
Only migrate tables from gettweets.

Avoid doing migration from view scripts like the search api as they'll
likely be time limited. Running from the CLI in gettweets should not be
time limited, so there's a better chance of the modifications
completing.
Use utf8_general_ci for case insensitive searches.
Add a conversation API endpoint.
Lookup the initial id, and replies to it.
Lookup first tweet in all cases.

Avoid duplicate queries, and loop over all results in fetchInReplyTo
method.