Add is_curie() and is_uri() methods as helper functions

[matentzn]

Compression and expansion are not the only use cases for curies, we sometimes just want to know if a string is a curie or not. I keep writing wrappers with curies.parse... methods and it would be nice if this was somehow natively supported.

[cthoyt]

Related #77

[cthoyt]

question: you want this as a method of the converter or a generic one? It would be much easier to make it part of the converter.

[cthoyt]

@matentzn can you add some details on places where you would like to use this functionality?

[matentzn]

In OAK, the relationships are randomly curies when the URI prefix is known (is in the map) and URIs otherwise. For certain applications, I just want to skip all cases where the relationships don't have a valid entry in the prefix map.

But there are a lot of applications for example in data validation, where I want to spit a warning when something is a URI but should be a curie.