Improve error raising and add initial tests

test/description/output_2/desc_aryion.txt

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+:iconUserAryion:
+
+ -> :iconEkaPerson: :iconEkaPerson:
+[url=https://furaffinity.net/user/FaPerson]FaName[/url] [url=https://furaffinity.net/user/FaPerson]FaPerson[/url]
+[url=https://inkbunny.net/IbPerson]IbName[/url] [url=https://inkbunny.net/IbPerson]IbPerson[/url]
+[url=https://sfperson.sofurry.com]SfName[/url] [url=https://sfperson.sofurry.com]SfPerson[/url]
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/aryion]Link[/url]

test/description/output_2/desc_furaffinity.txt

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+:iconUserFuraffinity:
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+ -> :iconFaPerson: :iconFaPerson:
+[url=https://inkbunny.net/IbPerson]IbName[/url] [url=https://inkbunny.net/IbPerson]IbPerson[/url]
+[url=https://sfperson.sofurry.com]SfName[/url] [url=https://sfperson.sofurry.com]SfPerson[/url]
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/furaffinity]Link[/url]

test/description/output_2/desc_inkbunny.txt

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+[iconname]UserInkbunny[/iconname]
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+[fa]FaPerson[/fa] [fa]FaPerson[/fa]
+ -> [iconname]IbPerson[/iconname] [iconname]IbPerson[/iconname]
+[sf]SfPerson[/sf] [sf]SfPerson[/sf]
+[weasyl]weasylperson[/weasyl] [weasyl]weasylperson[/weasyl]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/inkbunny]Link[/url]

test/description/output_2/desc_sofurry.txt

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+:iconUserSoFurry:
+
+[url=https://aryion.com/g4/user/EkaPerson]EkaName[/url] [url=https://aryion.com/g4/user/EkaPerson]EkaPerson[/url]
+fa!FaPerson fa!FaPerson
+ib!IbPerson ib!IbPerson
+ -> :iconSfPerson: :iconSfPerson:
+[url=https://www.weasyl.com/~weasylperson]WeasylName[/url] [url=https://www.weasyl.com/~weasylperson]WeasylPerson[/url]
+[url=https://twitter.com/XPerson]XName[/url] [url=https://twitter.com/XPerson]XPerson[/url]
+[url=https://example.com/@MastodonPerson]MastodonName[/url] [url=https://example.com/@MastodonPerson]MastodonPerson@example.com[/url]
+[url=https://example.net/GenericPerson]GenericName[/url]
+
+[url=https://example.com/sofurry]Link[/url]

test/description/output_2/desc_weasyl.md

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+<!~UserWeasyl>
+
+[EkaName](https://aryion.com/g4/user/EkaPerson) [EkaPerson](https://aryion.com/g4/user/EkaPerson)
+<fa:FaPerson> <fa:FaPerson>
+<ib:IbPerson> <ib:IbPerson>
+<sf:SfPerson> <sf:SfPerson>
+ -> <!~WeasylPerson> <!~WeasylPerson>
+[XName](https://twitter.com/XPerson) [XPerson](https://twitter.com/XPerson)
+[MastodonName](https://example.com/@MastodonPerson) [MastodonPerson@example.com](https://example.com/@MastodonPerson)
+[GenericName](https://example.net/GenericPerson)
+
+[Link](https://example.com/generic)