libripgrep: initial commit introducing libripgrep

libripgrep is not any one library, but rather, a collection of libraries
that roughly separate the following key distinct phases in a grep
implementation:

  1. Pattern matching (e.g., by a regex engine).
  2. Searching a file using a pattern matcher.
  3. Printing results.

Ultimately, both (1) and (3) are defined by de-coupled interfaces, of
which there may be multiple implementations. Namely, (1) is satisfied by
the `Matcher` trait in the `grep-matcher` crate and (3) is satisfied by
the `Sink` trait in the `grep2` crate. The searcher (2) ties everything
together and finds results using a matcher and reports those results
using a `Sink` implementation.

Closes #162

grep-pcre2/README.md

@@ -0,0 +1,39 @@
+grep-pcre2
+----------
+The `grep-pcre2` crate provides an implementation of the `Matcher` trait from
+the `grep-matcher` crate. This implementation permits PCRE2 to be used in the
+`grep` crate for fast line oriented searching.
+
+[![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-pcre2.svg)](https://crates.io/crates/grep-pcre2)
+
+Dual-licensed under MIT or the [UNLICENSE](http://unlicense.org).
+
+### Documentation
+
+[https://docs.rs/grep-pcre2](https://docs.rs/grep-pcre2)
+
+**NOTE:** You probably don't want to use this crate directly. Instead, you
+should prefer the facade defined in the
+[`grep`](https://docs.rs/grep)
+crate.
+
+If you're looking to just use PCRE2 from Rust, then you probably want the
+[`pcre2`](https://docs.rs/pcre2)
+crate, which provide high level safe bindings to PCRE2.
+
+### Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+grep-pcre2 = "0.1"
+```
+
+and this to your crate root:
+
+```rust
+extern crate grep_pcre2;
+```