Feature upload

[pbearne]

Pull Request Type

• [ X] I have checked there is no other PR open for the same change.

This is a:

• Bug fix
• [X ] New feature
• Code quality improvement

Context

Detailed Description

This is an update/refreshed version of https://github.com/soulseekah/Requests/tree/feature-upload

I have also added a helper function
Requests::add_files_to_body() to provide simplar way to add files to a body object

Quality assurance

• [ X] This change does NOT contain a breaking change (fix or feature that would cause existing functionality to change).
• [ x] I have commented on my code, particularly in hard-to-understand areas.
• [x ] I have added unit tests to accompany this PR.
• [x ] The (new/existing) tests cover this PR 100%.
• [x ] I have (manually) tested this code to the best of my abilities.
• [ x] My code follows the style guidelines of this project.

Documentation

For new features:

• [x ] I have added a code example showing how to use this feature to the examples directory.
• [x ] I have added documentation about this feature to the docs directory.
  If the documentation is in a new markdown file, I have added a link to this new file to the Docs folder README.md file.

#289

[gdarko]

Why this still isn't merged? Such useful features...

[jrfnl]

@gdarko It's kind of hard to review code which is littered with unaddressed (automated) comments....