Response headers, status code, and error handling

[oddwhocanfly]

Proposed handler fixes and error handling improvements for #315

The general idea is to render component into a buffer before writing it to response, so that in the event of error, error handler can write its own response with correct status code and headers. The buffer is obtained with GetBuffer() and component should be able to use it directly as if it obtained buffer on its own.

Additionally, handler now sets headers to header map before writing response code, and does not write response code when calling error handler so that it can set its own headers and response code.

[a-h]

I just did a minor refactor, as per @matryer's talk https://youtu.be/yeetIgNeIkc?si=7BiJMIsYe3Uvghjn&t=255

[a-h]

Thanks for that, much appreciated! I'm prepping for a release, just want to do some work on #249, a bit more testing, and I'll push it.

[oddwhocanfly]

Thank you! Yes, i did have a feeling that wasn't an idiomatic thing in go 🙂