noDuplicates() and preserveKeys

Add

• preserveKeys() during drawing sample from an associative array
• added some test in order to have coverage 100%

Change

• method unique(), allowDuplicates(), noDuplicates() for sequence generation;

range() and examples

Add

• range method for generating integer (shortcut for min and max)
• new examples, useful for new users
• add some notes how to launch test coverage
• add some warning in README specially for cryptographic usage (this is a pseudo random library).

Change

• improve the usage section in readme

New Random library

Fluent interface for extracting random sample and for generating number, byte, boolean, sequence.