SearchFilter with unaccent

[gdvalderrama]

Currently SearchFilter offers 4 restrictions:

• '^' Starts-with search.
• '=' Exact matches.
• '@' Full-text search. (Currently only supported Django's PostgreSQL backend.)
• '$' Regex search.

It would be great to have the possibility of using __unaccent lookup.

Example:

Search for "Héctor" would also return "Hector".