Add proper test crg file with closed refline

[CarawaySeed42]

Since the CRG standard supports a closed reference line and the behavior
of the API changes when such a refline is encountered (loop u value at start/end, rflc option, crg_check, ...),
the repository should contain at least one test CRG file with a closed refline and
the refline continuation flag set.

This makes testing the API on closed reflines easier.

[CarawaySeed42]

I am aware that crg-txt\handmade_circle.crg exists, but it is extremely basic and does not have the the refline continuation option set. It also does not have geographic coordinates or a map projection which both have been a source of bugs in the API in the past.