Add benchmarks for D's std.regex

It would be interesting to include benchmarks for D's std.regex.

I have initial work for it, but it is not ready to be a pull request, and I probably won't find the time to clean it up:

Branch: https://github.com/mrmonday/regex/tree/d-phobos-benchmarks Diff: https://github.com/rust-lang/regex/compare/master...mrmonday:d-phobos-benchmarks

General notes/notes for Rustaceans who don't read D:

Phobos is the name of D's standard library
There are 2*2 cargo features, which specify the compiler (ldc (LLVM) vs dmd (Digital Mars/Reference compiler)), and the regex mode - runtime (no extension), or generated at compile time (-ct). There's also a gdc (GNU based) compiler, but it's not in the arch repo's, so I didn't test it.
Various things are hardcoded/half-baked "just make it work"
There's a src/ffi/build_d.sh file with the commands needed to build things on the D side. These should be moved into the build.sh

Everything was built/tested using the ldc/dmd versions from the Arch Linux repositories

# ldc
LDC - the LLVM D compiler (1.6.0):
  based on DMD v2.076.1 and LLVM 5.0.0
  built with DMD64 D Compiler v2.077.0
# dmd
DMD64 D Compiler v2.077.1

Most of the regex is rather hackily parsed directly out of the Rust files on the D side at compile time, with some of the regex hard coded on the D side where it's anything but a string literal. It's probably easier/quicker to hard code it, but that's not what I did.
All the misc benchmarks run, most of sherlock runs (still some work to do), I haven't tested regexdna
Documentation for D's std.regex is here: https://dlang.org/phobos/std_regex.html

I'm happy to answer any questions to help this along, if I can.

rust-lang / regex

Add benchmarks for D's std.regex #430