Merge pull request #36 from microamp/master

Additional functions in fn.iters: compact and reject
Prevent pylint complains on Options
Preliminary implementation of immutable (persistent) heaps data structure (TODO: more tests, documentation)
Update haskell type definition, provided usage sampe from ipython
Fix error with PairingHeap creation of merge, introduce key and cmp functions as param
Test cases for key func for both heaps implementation
Provide link to "Union-based heaps" slides (KyivPy #11)
Test case for custom compare function
Preliminary implementation of linked list
Declare stack with familiar API: push and pop
Minor code formatting
Implement __lt__ callback for based heap class
Do not need to use __cmp__
Fix __nonzero__ behaviour in Python3+
Basic information about persistent data structure in README file
Adjust formatting for RST
Move adjustements and typo fixes
Do not need to highlight O(1) notation
Queue API declaration
Persistent queue data structure implementation based on two linked lists