Version 1.0 updates - Githubissues

Types of changes

This PR implements the following changes: (Please tick any or all of the following that are applicable)

[ ] :sparkles: New feature (A non-breaking change which adds functionality).
[ ] :bug: Bug fix (A non-breaking change, which fixes an issue).
[X] :boom: Breaking change (fix or feature that would cause existing functionality to change).

Key changes include alterations to the iterator code, since the iteration interface in Base is now different in julia v1.0.
The iterate method for an IntervalCollection now works like the Base.Iterators.Flatten iterate method.

[ ] :art: The changes implemented is consistent with the julia style guide.
[ ] :blue_book: I have updated and added relevant docstrings, in a manner consistent with the documentation styleguide.
[ ] :blue_book: I have added or updated relevant user and developer manuals/documentation in docs/src/.
[ ] :ok: There are unit tests that cover the code changes I have made.
[ ] :ok: The unit tests cover my code changes AND they pass.
[ ] :pencil: I have added an entry to the [UNRELEASED] section of the manually curated CHANGELOG.md file for this repository.
[ ] :ok: All changes should be compatible with the latest stable version of Julia.
[ ] :thought_balloon: I have commented liberally for any complex pieces of internal code.