nitg: executables not named .bin now

Signed-off-by: Jean Privat <jean@pryen.org>
lib: implements `Float::to_precision` in a non native way

Signed-off-by: Jean Privat <jean@pryen.org>
niti: add some Float extern methods

Signed-off-by: Jean Privat <jean@pryen.org>
ast: factorize `n_string` to `AStringFormExpr`

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

Signed-off-by: Jean Privat <jean@pryen.org>
phase: framework for global phases

Signed-off-by: Jean Privat <jean@pryen.org>
nitmetrics: implements metrics as global phases

Signed-off-by: Jean Privat <jean@pryen.org>
tests: really test nitmetrics.nit

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