Allow intralinks that do not start with `crate::`

[orium]

Currently we only support intralinks format with absolute paths from the root of the crate, i.e. links of the form [⋯](crate::⋯). This is an annoying limitation and users may think intralinks are broken alltogether (see #150).

[praveenperera]

this would be nice

[orium]

#177 solves this. I'm working on it on #236, but I've not been able to dedicate much time to it recently.

[praveenperera]

Maybe I can take that PR over? What needs to be done still?

[orium]

Sorry, this is too fundamental of a change for me to delegate to anyone else.

[praveenperera]

No problem, I get that