Support postgres

[fabioperrella]

related to #3
closes #11

This PR:

• adds support for PostgreSQL (unfortunately all results are uncertain)
• adds support for Ruby >= 2.5 and Activerecord >= 4
• sorts lines in the HTML report by certainity_level, identifier, query
• improves the query analyser to not analyse a query again if a similar query was analysed before with a prepared statement (Postgres use prepared statements as default)
• improves the logic to detect if a query was fired from a test file or not
• removes the auto require for the module TestHelpers

[fabioperrella]

@julik @lorenzograndi4 sorry I know this PR is huge!

If you could just take a quick look, I would appreciate it!

[julik]

Diagonal scan looks good 😆

Could it be an idea to try to install a "representative dataset" for testing the gem? For example using a fuller list of Brazilian municipalities + a longer list of people names, say generated with Faker. I suspect it is really dependent on the table size, both for MySQL and PostgerSQL, what the query planner will plan.

[fabioperrella]

Diagonal scan looks good 😆

Could it be an idea to try to install a "representative dataset" for testing the gem? For example using a fuller list of Brazilian municipalities + a longer list of people names, say generated with Faker. I suspect it is really dependent on the table size, both for MySQL and PostgerSQL, what the query planner will plan.

thank you!

Indeed, I also think that the results would be better if using more data, but this will not be the case when it analyses queries running on unit tests, for example.

I will create an issue with that, maybe an idea could be born influenced by that!