Split big sitemaps & generate proper index (closes #79, #106)

[stefandoorn]

• Split big sitemaps based on a configurable limit (defaults to 50.000)
• Use the amount of files in generation of the URIs to these files (and use them in the index)

[stefandoorn]

@loevgaard I started working on this. I'm not very happy yet with the implementation. For sure the command does too much, but that's a refactor for later. The sending around of the amount of paths to the index provider should be more elegant, but couldn't come up with a better implementation right now.

[next-sentence]

any estimation when it will be merged?

[bmehdi]

any estimation when it will be merged?

[stefandoorn]

Ah, haven't looked into it anymore. Have you maybe been able to test it in a real project? Would be great to have some feedback on the implementation.