Add ability to pass ebVLRs to the writer.

[bacek]

This allows to do full round-trip with parsing actual ebVLRs and then serializing them back.

[abellgithub]

I don't understand the purpose of this. You call these "user_vlr", but they are not user VLRs. The extra byte VLR MUST match the stored data -- I don't understand why a user should want to set this as it can lead to an invalid file.

[bacek]

I don't understand the purpose of this. You call these "user_vlr", but they are not user VLRs. The extra byte VLR MUST match the stored data -- I don't understand why a user should want to set this as it can lead to an invalid file.

My use case: we create extra dimensions for points and add VLR with correct name and description.

I can add assert that header.ebCount matches user_vlrs

[abellgithub]

The writer code in lazperf primarily exists to support testing. It's not intended to be used as a complete file writer -- there's no support for VLRs in general in lazperf. If this change is helpful to you, that's great and that's the intent of open source -- modify for your needs, but I'd need some convincing to turn lazperf into a more general LAZ file I/O package, which is what this is taking a step towards. I think I'd want a more general design if we were going to go down that road, rather than just support for user-provided EB VLRs.

[nigels-com]

Lack of general VLR support is a deal-breaker for our use cases. Just FYI.
LASzip is long in the tooth, but gets the job done.