Switch 'rojo build' to use BufWriter, magic performance increase

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Rojo Changelog
 
 ## [Unreleased]
+* Changed `rojo build` to use buffered I/O, which can make it up to 2x faster in some cases.
+    * Building [*Road Not Taken*](https://github.com/LPGhatguy/roads) to an `rbxlx` file dropped from 150ms to 70ms on my machine
 
 ## [0.5.0 Alpha 8](https://github.com/LPGhatguy/rojo/releases/tag/v0.5.0-alpha.8) (March 29, 2019)
 * Added support for a bunch of new types when dealing with XML model/place files:

server/src/commands/build.rs

@@ -1,7 +1,7 @@
 use std::{
     path::PathBuf,
     fs::File,
-    io,
+    io::{self, Write, BufWriter},
 };
 
 use log::info;
@@ -92,7 +92,7 @@ pub fn build(options: &BuildOptions) -> Result<(), BuildError> {
     let mut imfs = Imfs::new();
     imfs.add_roots_from_project(&project)?;
     let tree = construct_oneoff_tree(&project, &imfs)?;
-    let mut file = File::create(&options.output_file)?;
+    let mut file = BufWriter::new(File::create(&options.output_file)?);
 
     match output_kind {
         OutputKind::Rbxmx => {
@@ -121,5 +121,7 @@ pub fn build(options: &BuildOptions) -> Result<(), BuildError> {
         },
     }
 
+    file.flush()?;
+
     Ok(())
 }