Improve source & checksum system to allow multiple files

[Mia-Rain]

The current source & checksum system allows only a single binary and checksum to be specified, in the past one has gotten around this issue for patches using the following: https://github.com/skycocker/chromebrew/blob/7ff8d64879405832d7ac8eb70b208d431732abe7/packages/gtk_doc.rb#L34-L35

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This workaround does work well, but again, it's only a workaround, and a proper fix should be implemented.

I figure the current system could be reworked to use an array system, thus the current code could simply loop over the array. The idea comes from xbps-src, as they have a way of doing this;

distfiles="
http://www.docbook.org/sgml/$version/$pkgname-$version.zip
http://www.docbook.org/sgml/4.4/$pkgname-4.4.zip
http://www.docbook.org/sgml/4.3/$pkgname-4.3.zip
http://www.docbook.org/sgml/4.2/$pkgname-4.2.zip
http://www.oasis-open.org/docbook/sgml/4.1/docbk41.zip
http://www.oasis-open.org/docbook/sgml/4.0/docbk40.zip
http://www.oasis-open.org/docbook/sgml/3.1/docbk31.zip
http://www.oasis-open.org/docbook/sgml/3.0/docbk30.zip
http://www.oasis-open.org/docbook/sgml/2.4.1/docbk241.zip"
checksum="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"

https://github.com/void-linux/void-packages/blob/master/srcpkgs/docbook/template#L11-L29

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Although I personally don't know ruby well enough to fix it, there has to be someone who does within our project group!

[uberhacker]

@ThatGeekyWeeb: We do something very similar to this in install.sh.