Support read file from http URL

[hudeven]

Motivation and Context

1. We want to read pre-train model files from a public http/https URL using PathManager
2. As fvcore is available in PyPI, we should add it as dependency, such that we can use HTTPURLHandler to read http/https URL

#1220

How Has This Been Tested

I'm able to download model file in Python Console. I'm not adding a unit test as it adds complexity to exclude the test for internal use case.

with PathManager.open("https://dl.fbaipublicfiles.com/pytext/models/roberta/roberta_public.pt1", "rb") as f:
... print(len(f.read()))
...
roberta_public.pt1: 9%|█████▊ | 44.4M/497M [00:07<01:22, 5.47MB/s]
roberta_public.pt1: 497MB [01:19, 6.25MB/s]
497003753

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

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@hudeven has updated the pull request. Re-import the pull request

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@hudeven has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

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@hudeven merged this pull request in ba1b16e.