Add `fsm_generate_matches` to cli

[silentbicycle]

This adds a -G <max_length> option to re and fsm.

Also, add a default / basic use case callback, fsm_generate_cb_printf, which is what re and fsm use.

[silentbicycle]

CI failed because of https://github.com/katef/kmkf/issues/14 , rerunning.

[silentbicycle]

CI failed again, because of katef/kmkf#14 , rerunning again.

[katef]

Sample output:

; ./build/bin/re -r pcre -G 5 '^a[0-9]*b?c'
abc
abc!
abc!!
ac
ac!
ac!!
ac!!!
a0bc
a0bc!
a0c
a0c!
a0c!!
a00c
a00c!