Changelog:

• Added support for Python 3.8.
• Add __slots__ optimization in Node class, should give performance improvement.
• Fixed:
  • Restore universal wheels.
  • Bytes/str type incompatibility in setup.py.
  • New version of distutils rejects version suffixes of .postNN, use aNN instead.

Depends on D9592

Signed-off-by: Algent Albrahimi <algent@protonmail.com>

• Update spyder3 and run a few scripts.
• Run these examples using cli:

>>> from intervaltree import Interval, IntervalTree
>>> t = IntervalTree()
>>> t
IntervalTree()
>>> t[1:2] = "1-2"
>>> t[4:7] = (4, 7)
>>> t[5:9] = {5: 9}
>>> sorted(t[6])
[Interval(4, 7, (4, 7)), Interval(5, 9, {5: 9})]
>>> sorted(t[6])[0]
Interval(4, 7, (4, 7))
>>> sorted(t[2:4])
[]
>>> sorted(t[1:5])
[Interval(1, 2, '1-2'), Interval(4, 7, (4, 7))]
>>> sorted(t.envelop(1, 5))
[Interval(1, 2, '1-2')]