Changelog:
- Add education level to all queries

- Add route '/education_level' to query the available education levels.
  The response is a set of pairs (id, education_level)

- Change var declarations to their respective const and let counterparts

- Fix wrong foreign key name in the aggregation by states. When a
  adm_dependency_id parameter was supplied, the query would fail.

Changes:
- Add error handling in the database query function. When a database error
occurs, it is logged in the server and a plain text response is returned to the
user.
- Implement the building of queries inside the API, which removes the
  need to have stored functions/procedures on the database, which is not
  flexible or efficient to maintain/extend.
- Use route chaining to determine which function will build the query
  that needs to be executed. The last function is the one that actually
  sends the query to the database and send the response.

Future Work:
- Instead of returning a plain text response, return a HTTP 501 status,
  which is currently not possible. When one attempts to send such status
  the framework throws an error that the headers were already sent for
  the current request.
- Chaining based on the route might not be the best solution here.

Signed-off-by: João Victor Tozatti Risso <jvtr12@c3sl.ufpr.br>

Signed-off-by: João Victor Tozatti Risso <jvtr12@c3sl.ufpr.br>

Closes #6

Signed-off-by: João Victor Tozatti Risso <jvtr12@c3sl.ufpr.br>

Signed-off-by: João Victor Tozatti Risso <jvtr12@c3sl.ufpr.br>

- Rename /matriculas to /enrollments
- Add initial support for parameters in the enrollments route

Related: #3

Signed-off-by: João Victor Tozatti Risso <jvtr12@c3sl.ufpr.br>

Implement the following aggregations:
- per-state
- per-region
- country

In order to use these queries one should use the /api/v1/matriculas route. When
the 'agregar' query parameter is set, one could use the values 'estado' and 'regiao'
to run the aggregation for state and region, respectively. Otherwise, if no parameters
are supplied, it defaults to the whole country aggregation query.

Not following any specs