auto merge of #13700 : BurntSushi/rust/regexp, r=alexcrichton

Implements [RFC 7](https://github.com/rust-lang/rfcs/blob/master/active/0007-regexps.md) and will hopefully resolve #3591. The crate is marked as experimental. It includes a syntax extension for compiling regexps to native Rust code.

Embeds and passes the `basic`, `nullsubexpr` and `repetition` tests from [Glenn Fowler's (slightly modified by Russ Cox for leftmost-first semantics) testregex test suite](http://www2.research.att.com/~astopen/testregex/testregex.html). I've also hand written a plethora of other tests that exercise Unicode support, the parser, public API, etc. Also includes a `regex-dna` benchmark for the shootout.

I know the addition looks huge at first, but consider these things:

1. More than half the number of lines is dedicated to Unicode character classes.
2. Of the ~4,500 lines remaining, 1,225 of them are comments.
3. Another ~800 are tests.
4. That leaves 2500 lines for the meat. The parser is ~850 of them. The public API, compiler, dynamic VM and code generator (for `regexp!`) make up the rest.

1 files changed, 79 insertions, 0 deletions

diff --git a/src/libregex/testdata/nullsubexpr.dat b/src/libregex/testdata/nullsubexpr.dat
new file mode 100644
index 00000000000..2e18fbb9170
--- /dev/null
+++ b/src/libregex/testdata/nullsubexpr.dat
@@ -0,0 +1,79 @@
+NOTE	null subexpression matches : 2002-06-06
+
+E	(a*)*		a		(0,1)(0,1)
+#E	SAME		x		(0,0)(0,0)
+E	SAME		x		(0,0)(?,?)	RE2/Go
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a*)+		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a+)*		a		(0,1)(0,1)
+E	SAME		x		(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a+)+		a		(0,1)(0,1)
+E	SAME		x		NOMATCH
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+
+E	([a]*)*		a		(0,1)(0,1)
+#E	SAME		x		(0,0)(0,0)
+E	SAME		x		(0,0)(?,?)	RE2/Go
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	([a]*)+		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	([^b]*)*	a		(0,1)(0,1)
+#E	SAME		b		(0,0)(0,0)
+E	SAME		b		(0,0)(?,?)	RE2/Go
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaab		(0,6)(0,6)
+E	([ab]*)*	a		(0,1)(0,1)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		ababab		(0,6)(0,6)
+E	SAME		bababa		(0,6)(0,6)
+E	SAME		b		(0,1)(0,1)
+E	SAME		bbbbbb		(0,6)(0,6)
+E	SAME		aaaabcde	(0,5)(0,5)
+E	([^a]*)*	b		(0,1)(0,1)
+E	SAME		bbbbbb		(0,6)(0,6)
+#E	SAME		aaaaaa		(0,0)(0,0)
+E	SAME		aaaaaa		(0,0)(?,?)	RE2/Go
+E	([^ab]*)*	ccccxx		(0,6)(0,6)
+#E	SAME		ababab		(0,0)(0,0)
+E	SAME		ababab		(0,0)(?,?)	RE2/Go
+
+E	((z)+|a)*	zabcde		(0,2)(1,2)
+
+#{E	a+?		aaaaaa		(0,1)	no *? +? mimimal match ops
+#E	(a)		aaa		(0,1)(0,1)
+#E	(a*?)		aaa		(0,0)(0,0)
+#E	(a)*?		aaa		(0,0)
+#E	(a*?)*?		aaa		(0,0)
+#}
+
+B	\(a*\)*\(x\)		x	(0,1)(0,0)(0,1)
+B	\(a*\)*\(x\)		ax	(0,2)(0,1)(1,2)
+B	\(a*\)*\(x\)		axa	(0,2)(0,1)(1,2)
+B	\(a*\)*\(x\)\(\1\)	x	(0,1)(0,0)(0,1)(1,1)
+B	\(a*\)*\(x\)\(\1\)	ax	(0,2)(1,1)(1,2)(2,2)
+B	\(a*\)*\(x\)\(\1\)	axa	(0,3)(0,1)(1,2)(2,3)
+B	\(a*\)*\(x\)\(\1\)\(x\)	axax	(0,4)(0,1)(1,2)(2,3)(3,4)
+B	\(a*\)*\(x\)\(\1\)\(x\)	axxa	(0,3)(1,1)(1,2)(2,2)(2,3)
+
+#E	(a*)*(x)		x	(0,1)(0,0)(0,1)
+E	(a*)*(x)		x	(0,1)(?,?)(0,1)	RE2/Go
+E	(a*)*(x)		ax	(0,2)(0,1)(1,2)
+E	(a*)*(x)		axa	(0,2)(0,1)(1,2)
+
+E	(a*)+(x)		x	(0,1)(0,0)(0,1)
+E	(a*)+(x)		ax	(0,2)(0,1)(1,2)
+E	(a*)+(x)		axa	(0,2)(0,1)(1,2)
+
+E	(a*){2}(x)		x	(0,1)(0,0)(0,1)
+E	(a*){2}(x)		ax	(0,2)(1,1)(1,2)
+E	(a*){2}(x)		axa	(0,2)(1,1)(1,2)