added FileIO interface

[jonathanBieler]

A clear and descriptive title (No issue numbers please)

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Types of changes

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

• ✨ New feature (A non-breaking change which adds functionality).
• 🐛 Bug fix (A non-breaking change, which fixes an issue).
• 💥 Breaking change (fix or feature that would cause existing functionality to change).

📋 Additional detail

Adds support for FileIO interface :

using BED, FileIO

FileIO.load("/mnt/ssd_disk/.julia/packages/FormatSpecimens/cmrLJ/BED/itemRgb.bed")

☑️ Checklist

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

[jonathanBieler]

The test fails because FileIO doesn't know about .bed (yet...).

[kescobo]

This is awesome 👍

[kescobo]

If FileIO is only used in the extension, I don't think we want it in the main deps sections

[jonathanBieler]

Right, I removed it.

[kescobo]