docdowm: empty lignes are included in blocks

Signed-off-by: Jean Privat <jean@pryen.org>
nitunit: test only block of code

Signed-off-by: Jean Privat <jean@pryen.org>
nitunit: protect generated files name a little to avoid name conflicts.

Signed-off-by: Jean Privat <jean@pryen.org>
tests: update and improve tests for nitunit

Signed-off-by: Jean Privat <jean@pryen.org>