Upgrade to the 2018 edition

I didn't think it'd be this useful first, but thank god for `cargo fix --edition`!

src/header/stdlib/lcg48.rs

@@ -1,6 +1,6 @@
 //! Helper functions for pseudorandom number generation using LCG, see https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/functions/drand48.html
 
-use platform::types::*;
+use crate::platform::types::*;
 
 /* The default element buffer for the linear congruential generator's
  * sequence. Implemented using a c_ushort array for consistency between

src/header/stdlib/mod.rs

@@ -7,20 +7,20 @@ use rand::prng::XorShiftRng;
 use rand::rngs::JitterRng;
 use rand::{Rng, SeedableRng};
 
-use c_str::CStr;
-use fs::File;
-use header::errno::*;
-use header::fcntl::*;
-use header::limits;
-use header::string::*;
-use header::time::constants::CLOCK_MONOTONIC;
-use header::time::timespec;
-use header::unistd::{sysconf, _SC_PAGESIZE};
-use header::wchar::*;
-use header::{ctype, errno, unistd};
-use platform;
-use platform::types::*;
-use platform::{Pal, Sys};
+use crate::c_str::CStr;
+use crate::fs::File;
+use crate::header::errno::*;
+use crate::header::fcntl::*;
+use crate::header::limits;
+use crate::header::string::*;
+use crate::header::time::constants::CLOCK_MONOTONIC;
+use crate::header::time::timespec;
+use crate::header::unistd::{sysconf, _SC_PAGESIZE};
+use crate::header::wchar::*;
+use crate::header::{ctype, errno, unistd};
+use crate::platform;
+use crate::platform::types::*;
+use crate::platform::{Pal, Sys};
 
 mod lcg48;
 mod sort;

src/header/stdlib/sort.rs

@@ -1,4 +1,4 @@
-use platform::types::*;
+use crate::platform::types::*;
 
 pub fn introsort(
     base: *mut c_char,