FAQ: Note that update-guestfs-appliance is not needed with libguestfs >= 1.26.
tests: Don't use relative paths to binaries in tests.

All tests run under the ./run binary.  For a long time the ./run
binary has set the $PATH environment variable to contain all of the
directories with binaries in them.

Therefore there is no reason to use ../fish/guestfish instead of just
plain guestfish (and the same applies to other built binaries).
generator: Change type of 'tests' to 'c_api_tests'.

Just a code refactoring, has no functional effect.
v2v: Document the input: output: and convert: features in --machine-readable output.