For CoAP, there is actually a difference between
`/some/path` and `/some/path/`. This needs to be reflected
when parsing the URI and location path options from a given
string.
- add generic string put and get functions
- add location path and location query options
- add dedicated functions for getting and setting
URI query, URI path, location query, and location path
options
The nanocoap_get function is refactored to split of the request part
into a separate function for reuse by other modules. Support for
retransmissions when the received frame is malformed is dropped as it
was broken anyway.
