reworked original 2.x version of xrange into range

Fixes #50.
```
changed from int to BigInteger to support ranges beyond 2^64
added applicable test from stdlib
added convenience methods to iptest/assert_util.py to mimic unittest
added slice operator
added == != < <= > >= operators
added __contains__ method
added count and index methods of collections.abc.Sequence
changed start, stop and step to be attributes
added __hash__
added support for objects implementing __index__
```
Outstanding: pickle testing - it depends on itertools which depends on missing language features
I also made a change to Builtin (int is BigInteger) which may need to wait until a real int->long unification is done.
When reviewing, go for second commit otherwise rename obfuscates changes.

The result test out of a branch with some other temporary work around:
```
rejap@WIN-CUE1I6EN9JB ~/github/ironpython3/bin/Debug
$ ./IronPythonTestConsole.exe  IronPythonTest -noh -labels -full -test:IronPythonTest.Cases.IronPythonCases.test_range                 Runtime Environment -
    OS Version: Microsoft Windows NT 6.1.7601 Service Pack 1
  .NET Version: 4.0.30319.18444

***** IronPythonTest.DLL
***** IronPythonCases
***** IronPythonTests
***** test_range
>>>   0.00s testing test_attributes_from_stdlib
>>>   0.25s testing test_comparison_from_stdlib
>>>   0.45s testing test_contains_from_stdlib
>>>   0.51s testing test_count_from_stdlib
>>>   0.58s testing test_empty_from_stdlib
>>>   0.58s testing test_index_from_stdlib
>>>   0.71s testing test_invalid_invocation_from_stdlib
>>>   0.94s testing test_issue11845_from_stdlib
>>>   1.04s testing test_odd_bug_from_stdlib
>>>   1.05s testing test_range
>>>   1.10s testing test_range_collections
>>>   1.12s testing test_range_corner_cases
>>>   1.17s testing test_range_coverage
>>>   1.21s testing test_range_equal
>>>   1.21s testing test_range_from_stdlib
>>>   1.26s testing test_repr_from_stdlib
>>>   1.26s testing test_reverse_iteration_from_stdlib
>>>   1.29s testing test_slice_from_stdlib
>>>   1.33s testing test_strided_limits_from_stdlib
>>>   1.34s testing test_types_from_stdlib
>>>   1.47s testing test_user_index_method_from_stdlib

21 tests passed
Tests run: 1, Passed: 1, Errors: 0, Failures: 0, Inconclusive: 0
  Not run: 0, Invalid: 0, Ignored: 0, Skipped: 0
Elapsed time: 00:00:11.9180000
```