Implementation of collision resistant hash table. This is a hash table
 that provides a reliable (what you add there stays there, and duplicate
 keys are allowed) with as fast reference to the key as possible. If
 there are a lot of duplicate keys in the hash table the lookup gets
 slower of course. However, this is reliable and no data is lost at any
 point. If you know that you never have duplicate keys then this is as
 fast as any simple hash table.

 The interface provides many ways to search the hash table including
 an extended interface where caller can specify its own hash and comparison
 functions.

 There are two ways to traverse the entire hash table if this feature
 is needed. There exists a foreach function that calls a foreach
 callback for each entry in the hash table. Other way is to use
 SilcHashTableList structure and traverse the hash table inside while()
 using the list structure. Both are equally fast.

 The hash table is not thread safe.  If same hash table context is used in
 multi thread environment concurrency control must be employed.