Keep indices when dropping/renaming columns.
Add func to fetch SQL definition for indices.

Also rearrange sql.Result and err declaration.
Fix index operations:

- Pass args as variadic params
- Tests for index operations
- Refactor fetchColumns
Refactor columns matching method
Add shell script to generate migration script.
Merge pull request #99 from fudanchii/migration

Fix Indices Related Operation at Migration
Run drone as drone user, added --purge code for complete uninstall
Adapted README.md: 8080 is now default port for upstart service
Adapted new user creation on make install