Missing lengths for purl parts / and purl as a whole

[xSeagullx]

Hey!

I did not find anything about the max length of purl, which is quite important, for example if you need that purl to be stored in relational databases.

[pombredanne]

@xSeagullx as explained in #289 (comment) there is no length we can set for purl parts (aka. components). Some ecosystems may have their own limits that we could specify in a purl type definition for reference, but unless someone can come with the list of limits for a type, (and preferably all types) there is nothing we can do much.

I am therefore moving this to a discussion so we can explore this further.