Assert a ::std::fs::read_to_string(path) value is less than or equal to an expression.
Pseudocode:
std::fs::read_to_string(path) ≤ expr
§Example
use assertables::*;
let path = "alfa.txt";
let value = String::from("bravo\n");
assert_fs_read_to_string_le!(&path, &value);
§Module macros