Remove unnecessary 'extern crate's in Rust 2018 edition, import macros

https://rust-lang-nursery.github.io/edition-guide/print.html#no-more-extern-crate
https://rust-lang-nursery.github.io/edition-guide/rust-2018/macros/macro-changes.html
https://github.com/iceiix/steven/pull/13#issuecomment-435702507

blocks/src/lib.rs

@@ -1,15 +1,12 @@
 
 #![recursion_limit="300"]
 
-extern crate cgmath;
-extern crate collision;
-#[macro_use]
-extern crate lazy_static;
 extern crate steven_shared as shared;
 
 use crate::shared::{Axis, Direction, Position};
 use collision::Aabb3;
 use cgmath::Point3;
+use lazy_static::lazy_static;
 
 pub mod material;
 pub use self::material::Material;

gl/build.rs

@@ -1,6 +1,3 @@
-extern crate gl_generator;
-extern crate khronos_api;
-
 use std::env;
 use std::fs::File;
 use std::io::BufWriter;

src/main.rs

@@ -14,29 +14,8 @@
 
 #![recursion_limit="300"]
 
-extern crate sdl2;
-extern crate zip;
-extern crate image;
 use std::time::{Instant, Duration};
-extern crate byteorder;
-#[macro_use]
-extern crate serde_json;
-extern crate aes;
-extern crate cfb8;
-extern crate sha1;
-extern crate reqwest;
-extern crate flate2;
-extern crate rand;
-extern crate hex;
-extern crate base64;
-extern crate cgmath;
-#[macro_use]
-extern crate log;
-#[macro_use]
-extern crate lazy_static;
-extern crate collision;
-extern crate rsa_public_encrypt_pkcs1;
-pub extern crate steven_blocks;
+use log::info;
 extern crate steven_shared as shared;
 
 #[macro_use]

src/model/mod.rs

@@ -15,6 +15,7 @@ use serde_json;
 
 use std::hash::BuildHasherDefault;
 use crate::types::hash::FNVHash;
+use log::{error};
 
 use rand::Rng;
 use image::GenericImageView;

src/protocol/mojang.rs

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 use sha1::{self, Digest};
-use serde_json;
+use serde_json::json;
 use reqwest;
 
 #[derive(Clone, Debug)]

src/render/mod.rs

@@ -32,6 +32,7 @@ use serde_json;
 use cgmath::prelude::*;
 use crate::world;
 use collision;
+use log::{error, trace};
 
 use std::hash::BuildHasherDefault;
 use crate::types::hash::FNVHash;

src/server/mod.rs

@@ -32,6 +32,7 @@ use crate::types::Gamemode;
 use crate::shared::{Axis, Position};
 use crate::format;
 use rsa_public_encrypt_pkcs1;
+use log::{error, debug, warn};
 
 mod sun;
 pub mod plugin_messages;

src/world/biome.rs

@@ -1,5 +1,6 @@
 
 use image::Rgba;
+use lazy_static::lazy_static;
 
 #[derive(Clone, Copy)]
 pub struct Biome {