str: add _STR_STATIC_INITIALIZER which takes a length as well
str: add _STR_STATIC_INITIALIZER which takes a length as well

It's really an internal interface since there isn't anything preventing the
user from supplying a mismatching length.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc