add uninstall feature

add this to formcorral.install file -

function formcorral_uninstall() {
watchdog("info", "uninstalling formcorral - removing tables");
$queries = array("DROP TABLE {formcorral}",
"DROP TABLE {formcorral_recipients}",
"DROP TABLE {formcorral_fields}",
"DROP TABLE {formcorral_submission}",
"DROP TABLE {formcorral_submission_values}",
"DROP TABLE {formcorral_validators}"
);
foreach ($queries as $query) {
db_query($query);
}
}