Elixir Berlin February Meetup Conditional context for macros

ecto_psql_extras: "null_indexes" method added

https://github.com/pawurb/ecto_psql_extras#null_indexes New release of EctoPSQLExtras library introduces a “null_indexes” method. It allows you to track indexes that contain mostly NULL values and can probably be changed to partial index to improve insert performance and reduce disk usage