Release 1.6.0

Digest release 1.6.0 is a bugfix release.
The following two bugs in the MT random number generator class have been fixed:

1. A small range close to Int.max like

   randomInt(in: Int.max - 5 ... Int.max)

   would crash the application

2. In extremely rare cases randomInt or randomUInt would return

   range.lowerBound - 1 or range.upperBound + 1

   as result