ni_nitdoc: do not reset modelbuilder options

we need the -I and others

Signed-off-by: Jean Privat <jean@pryen.org>
ni_nitdoc: arguments are what remains after process_options

Signed-off-by: Jean Privat <jean@pryen.org>
ni_nitdoc: print usage synopsys

Signed-off-by: Jean Privat <jean@pryen.org>
tests: remove some old .skip entries

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add nitx.nit and ni_nitdoc.nit to sav/

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'ni_nitdoc_tests'