grep-cli: introduce new grep-cli crate

This commit moves a lot of "utility" code from ripgrep core into
grep-cli. Any one of these things might not be worth creating a new
crate, but combining everything together results in a fair number of a
convenience routines that make up a decent sized crate.

There is potentially more we could move into the crate, but much of what
remains in ripgrep core is almost entirely dealing with the number of
flags we support.

In the course of doing moving things to the grep-cli crate, we clean up
a lot of gunk and improve failure modes in a number of cases. In
particular, we've fixed a bug where other processes could deadlock if
they write too much to stderr.

Fixes #990

src/main.rs

@@ -1,7 +1,5 @@
-extern crate atty;
 #[macro_use]
 extern crate clap;
-extern crate globset;
 extern crate grep;
 extern crate ignore;
 #[macro_use]
@@ -10,14 +8,11 @@ extern crate lazy_static;
 extern crate log;
 extern crate num_cpus;
 extern crate regex;
-extern crate same_file;
 #[macro_use]
 extern crate serde_json;
 extern crate termcolor;
-#[cfg(windows)]
-extern crate winapi_util;
 
-use std::io;
+use std::io::{self, Write};
 use std::process;
 use std::sync::{Arc, Mutex};
 use std::time::Instant;
@@ -33,13 +28,10 @@ mod messages;
 mod app;
 mod args;
 mod config;
-mod decompressor;
-mod preprocessor;
 mod logger;
 mod path_printer;
 mod search;
 mod subject;
-mod unescape;
 
 type Result<T> = ::std::result::Result<T, Box<::std::error::Error>>;