Add note about character encoding support.
Add note about Rails 4.1 and ActiveRecord `count`.
Put methods in module to prevent naming collisions.
Add note about :maxmind_local with SQL DB.
Revert "Merge pull request #628 from jzelenkov/fix-postresql-oid"

This reverts commit 2a29613acda2468e23056921cc257252d2128ea8, reversing
changes made to c5c459409db3163cd2d4670506c3c7575ae9af22.