new filter :: LDAPresolve.

As we had the need to resolve user name, and unix group from some application logs with just the uidNumber, we developed a logstash plugin to fullfill our needs.

https://github.com/EricDeveaud/logstash_filter_LDAPresolve
https://rubygems.org/gems/logstash-filter-LDAPresolve

I would like to have feedback, review, tests, comments and suggestion on this one.

Regards
## Example

assume we have on LDAPS (with no authent) an user John DOE with uidNumber 25377 that pertains to group nobody For example with following envent structure.

```
{
"@version" => "1",
"@timestamp" => "2015-06-29:00:00.000Z",
"some_infos" => 'foo bar"
}
```

and the following init configuration

```
LDAPresolve {
uidNumber => 25377
host => "ldaps.pasteur.fr"
userdn => "ou=utilisateurs,dc=pasteur,dc=fr"
groupdn => "ou=entites,ou=groupes,dc=pasteur,dc=fr"
}
```

we will get this output

```
{
"@version" => "1",
"@timestamp" => "2015-06-29:00:00.000Z",
"some_infos" => 'foo bar"
"user" => "John DOE"
"group" => "nobody"
"login" => "jdoe"
}
```