Wireup http custom headers in fetch options

[ramshenai]

Summary

• Expose custom headers for GitFetchOptions for Fetch, and indirectly for CloneOptions
  • Allows you to set extra headers
  • Note: Libgit2 sets some headers for HTTP requests (User-Agent, Host, Accept, Content-Type, Transfer-Encoding, Content-Length, Accept) that cannot be overriden.
  • Libgit2 reference: https://libgit2.github.com/libgit2/#HEAD/type/git_fetch_options
• Had to wrap these custom headers with GitFetchOptionsWrapper to dispose them. (Similar to how GitCheckoutOptsWrapper)

Tests

• Unit-tests, Added coverage in CloneFixture .& FetchFixture. the malformed/reserved headers are handled by libgit2, so you can validate them getting passed through to libgit2.
• Manual verification, tested against git-server

[ethomson]

Awesome, thanks for contributing this! I'm a little busy this weekend, but I'll try to take a look at this soon. Thanks!

[ramshenai]

Hello @ethomson, I was wondering if you had a chance to take a look?

Thanks!

[64bits]

I'd like to use custom authorization headers, need this PR to get merged!

[ethomson]

Looks good to me - thanks for contributing this!