repo: move all source code in crates directory

The top-level listing was just getting a bit too long for my taste. So
put all of the code in one directory and shrink the large top-level mess
to a small top-level mess.

NOTE: This commit only contains renames. The subsequent commit will
actually make ripgrep build again. We do it this way with the naive hope
that this will make it easier for git history to track the renames.
Sigh.

crates/grep/README.md

@@ -0,0 +1,41 @@
+grep
+----
+ripgrep, as a library.
+
+[![Linux build status](https://api.travis-ci.org/BurntSushi/ripgrep.svg)](https://travis-ci.org/BurntSushi/ripgrep)
+[![Windows build status](https://ci.appveyor.com/api/projects/status/github/BurntSushi/ripgrep?svg=true)](https://ci.appveyor.com/project/BurntSushi/ripgrep)
+[![](https://img.shields.io/crates/v/grep.svg)](https://crates.io/crates/grep)
+
+Dual-licensed under MIT or the [UNLICENSE](http://unlicense.org).
+
+
+### Documentation
+
+[https://docs.rs/grep](https://docs.rs/grep)
+
+NOTE: This crate isn't ready for wide use yet. Ambitious individuals can
+probably piece together the parts, but there is no high level documentation
+describing how all of the pieces fit together.
+
+
+### Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+grep = "0.2"
+```
+
+and this to your crate root:
+
+```rust
+extern crate grep;
+```
+
+
+### Features
+
+This crate provides a `pcre2` feature (disabled by default) which, when
+enabled, re-exports the `grep-pcre2` crate as an alternative `Matcher`
+implementation to the standard `grep-regex` implementation.