Support of Notepad++ v8.3 and later versions.

• Correct icons for light and dark themes, Notepad++ ≥ 8.0 (#18)
• Fixed icon for older versions
• Merged forms Open and Save into the single one (#15)

• Async UI, #14
• Pagination, #13
• Fixed "Deprecation notice for authentication", #12
• Fixed some "Argument out of range" exceptions, #10
• Downgrade .NET Framework to support old systems (4.7.2 -> 4.5)

• Update framework (4.5 -> 4.7.2)
• Simplify infrastructure

• Save loaded files to Document directory.

• Fixed error " Could not create SSL/TLS secure channel." in connection with GitHub.

• Added x64 version.
• Moved infrastructure into the separated project (NppNetInf).
• Integrated into AppVeyor CI system.
• Save to secret Gist by default.

• Fixed gists saving.
• Dependencies updated.
• Removed dependency on installed VS C++.
• Show version in About window.