Allow combined logical groups to generate working queries

[xjunior]

Allow combined logical groups. I.e.:

filter=(name.givenName eq "Jane" OR name.givenName eq "Jaden") and (name.familyName co "avi" or name.familyName ew "ith")

Without this fix, the parser assumes it can't process a logical operation at the end of a group.

With this fix it produces the following SQL:

SELECT "mock_users".*
FROM "mock_users"
WHERE ("mock_users"."first_name" ILIKE 'Jane' OR "mock_users"."first_name" ILIKE 'Jaden')
    AND ("mock_users"."last_name" ILIKE '%avi%' OR "mock_users"."last_name" ILIKE '%ith')

[pond]

Nicely done. Great fix, merging. Thanks!

[pond]

@xjunior #61, #62, #65 and #66 now all merged and released as v2.5.0, then back-ported to V1 as v1.6.0. Thanks again for the contributions.