Intervaltree

- Dropped support for Python 3.4, added 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

- Fixed:
- On some systems, setup.py opened README.md with a non-unicode encoding. My fault for leaving the encoding flapping in the breeze. It's been fixed.

- Added:
- Travis testing for 3.7 and 3.8-dev. These needed OpenSSL, sudo and Xenial. 3.8-dev is allowed to fail.
- Fixed:
- PyPI wasn't rendering markdown because I didn't tell it what format to use.
- Python 2 wasn't installing via pip because of a new utils package. It has been zapped.
- Maintainers:
- TestPyPI version strings use `.postN` as the suffix instead of `bN`, and `N` counts from the latest tagged commit, which should be the last release
- Install from TestPyPI works via `make install-testpypi`

- Breaking:
- `search(begin, end, strict)` has been replaced with `at(point)`, `overlap(begin, end)`, and `envelop(begin, end)`
- `extend(items)` has been deleted, use `update(items)` instead
- Methods that take a `strict=True/False` argument now consistently default to `strict=True`
- Dropped support for Python 2.6, 3.2, and 3.3
- Add support for Python 3.5, 3.6, and 3.7
- Faster `Interval` overlap checking (tuxzz, 56)
- Updated README:
- new restructuring methods from 2.1.0
- example of `from_tuples()` added
- more info about `chop()`, `split_overlaps()`, `merge_overlaps()` and `merge_equals()`.
- Fixes:
- `Node.from_tuples()` will now raise an error if given an empty iterable. This should never happen, and it should error if it does.
- `Interval.distance_to()` gave an incorrect distance when passed the `Interval`'s upper boundary
- `Node.pop_greatest_child()` sometimes forgot to `rotate()` when creating new child nodes. (escalonn, 41, 42)
- `IntervalTree.begin()` and `end()` are O(1), not O(n). (ProgVal, 40)
- `intersection_update()` and `symmetric_difference()` and `symmetric_difference_update()` didn't actually work. Now they do.
- `collections.abc` deprecation warning no longer happens
- Maintainers:
- PyPi accepts Markdown! Woohoo!
- reorganize tests
- more tests added to improve code coverage (We're at 96%! Yay!)
- test for issue 4 had a broken import reference

- Added:
- `merge_overlaps()` method and tests
- `merge_equals()` method and tests
- `range()` method
- `span()` method, for returning the difference between `end()` and `begin()`
- Fixes:
- Development version numbering is changing to be compliant with PEP440. Version numbering now contains major, minor and micro release numbers, plus the number of builds following the stable release version, e.g. 2.0.4b34
- Speed improvement: `begin()` and `end()` methods used iterative `min()` and `max()` builtins instead of the more efficient `iloc` member available to `SortedDict`
- `overlaps()` method used to return `True` even if provided null test interval
- Maintainers:
- Added coverage test (`make coverage`) with html report (`htmlcov/index.html`)
- Tests run slightly faster

- Fix: Issue 27: README incorrectly showed using a comma instead of a colon when querying the `IntervalTree`: it showed `tree[begin, end]` instead of `tree[begin:end]`