StripedDictionary concurrency level adjustment

[epeshk]

Currently, StripedDictionary takes concurrencyLevel as a constructor argument and never grows in number of segments. This can lead to performance issues under high write load or with bad hash codes (divisible by concurrencyLevel).

StripedDictionary can grow in number of segments like a ConcurrentDictionary. The ability to grow should be configurable for cases where a fixed number of segments is preferred.