feat: cref implementation

[InFTord]

my current idea for crefs implementation is basically: make crefs work like a command that you can copy

[OoLunar]

To add missing context:

Discord recently added extended support for markdown. This includes headers and more specifically: hyperlinks. Additionally, Discord has had support for executing slash commands via copying (see image below.)

The idea here is to combine the two features to easily allow viewing other documentation referenced by cref in the XML docs.

• To create a hyperlink in Discord is the same as creating a hyperlink in markdown: [brackets with text inside](http://parenthesis.url)
• To create a clickable slash command, simply embed the slash command name with the slash command id: </about:1039719636058513434>

Using the methods above, we can combine the two to create text like the following:

[/documentation member:SendMessageAsync(string? content)](</documentation:1039719636058513434>)

which would render like such:

/documentation member:SendMessageAsync(string? content)

[InFTord]

24 minutes later: it doesn't work, thanks discord

[OoLunar]

After further investigation, we've discovered the following:

• You cannot hyperlink slash commands:

• You cannot add arguments to slash commands:

This makes this feature fundamentally impossible without changes from Discord. This issue will be reopened if Discord ever adds support for both of the above features.