Download + upload support

What's Changed

• Support for associated array query parameters by @gajddo00 in #38
• Download support by @matejmolnar in #33
• DocC documentation by @gajddo00 in #41
• [FIX] Download file location no longer exists by @gajddo00 in #47
• [FIX] Upload manager adjustments by @gajddo00 in #48
• Add multipart/form-data support by @tonyskansf in #44
• Data and file upload support by @tonyskansf in #43
• Update README.md by @cejanen in #49