add sitemap_file as a global option

[tlienart]

@mortenpi would you mind trying this out?

closes #1047 by adding a global variable sitemap_file if the user wants something else than sitemap(.xml).

config.md

+++
# ... rest
sitemap_file = "mySitemap"
# ... rest
+++

--> mySitemap.xml will be generated (instead of default sitemap.xml)

[mortenpi]

Yep, this is perfect! Thank you!

Just as some bikeshedding: the option could also be called sitemap_filename maybe, to make it clear that it should not be a path?

[tlienart]

Agreed, in the next version there are aliases for default variables which makes that stuff a bit easier (just add more aliases!) but agreed that filename is better, will add.

[tlienart]

added sitemap_filename and rss_filename as aliases for sitemap_file and rss_file. will merge now, thanks for the FR!

[mortenpi]

Thank you for implementing it!