Exception when start if CROW_ROUTE url not starts with /

[xandross389]

If character "/" is missed at the begining of URL param in CROW_ROUTE declaration app not starts and throw exception with ambiguous message:

example:

CROW_ROUTE(app, "api/v1/service/status")

causes exception:

terminate called after throwing an instance of 'std::runtime_error'
 what():   Internal error: Trie header should be simple!

I suggest check specific condition and that cause exception and show correspondent message to the user

[StefanoPetrilli]

@The-EDev this one can be closed