Http optimizations, less ram usage, code cleanup
I've significantly reduced the ram usage by setting a limit to the number of simultaneous http connections.
To "benchmark" this, I've searched "jazz", "radio", "" and "deejay".
Before: ~102MiB
After: ~55MiB
I also cleaned up some code. For example, I enabled isahc's json support, so json conversion is now easier and faster.