More verbose deserialization errors

[Iizuki]

Issue

Serde deserialization errors are generally difficult to debug. Often you have you have ton of search results and only a few of them cause problems. It can be difficult to pinpoint the problematic LDAP entries.

Current situation

Currently we just pass on whatever errors serde gives us.

Solution

We could probably enrich the serde errors by bundling them with the LDAP data it's trying to deserialize from. Or at least the DN.

Issue refs

I believe this would be a cleaner solution to #32 also.