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-regex/src/util.rs

@@ -0,0 +1,29 @@
+/// Converts an arbitrary sequence of bytes to a literal suitable for building
+/// a regular expression.
+pub fn bytes_to_regex(bs: &[u8]) -> String {
+    use std::fmt::Write;
+    use regex_syntax::is_meta_character;
+
+    let mut s = String::with_capacity(bs.len());
+    for &b in bs {
+        if b <= 0x7F && !is_meta_character(b as char) {
+            write!(s, r"{}", b as char).unwrap();
+        } else {
+            write!(s, r"\x{:02x}", b).unwrap();
+        }
+    }
+    s
+}
+
+/// Converts arbitrary bytes to a nice string.
+pub fn show_bytes(bs: &[u8]) -> String {
+    use std::ascii::escape_default;
+    use std::str;
+
+    let mut nice = String::new();
+    for &b in bs {
+        let part: Vec<u8> = escape_default(b).collect();
+        nice.push_str(str::from_utf8(&part).unwrap());
+    }
+    nice
+}