Begin work on v2.0.0

The original release of mmv took filenames as command line arguments,
opened them in an editor, and then used the saved changes to rename
files.  This commit begins work on a new version of mmv where files are
provided via the standard input and the command line arguments specify a
process to spawn.  The spawned process reads command line arguments from
the standard input, processes them, and prints new names to the standard
output.  Those new names represent the new file names.  Here are a few
example usages, some more useful than others.

Reverse file names:

    $ ls * | mmv rev

Edit file names in your editor (v1.0.0 behavior):

    $ ls * | mmv vipe

Number movies so they’re automatically sorted:

    $ ls movie1 movie2 ... movieN \
          | mmv awk '{ printf "%02d-%s\n", NR, $0 }'

1 files changed, 7 insertions, 0 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 6bb11ed..8fa39ec 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -30,6 +30,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "getopt"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee1289e6cb1ae7c28a9b9776bd599f8afb31c20965ff257a8ea20eaa4da5e3c7"
+
+[[package]]
 name = "instant"
 version = "0.1.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -57,6 +63,7 @@ checksum = "fc7fcc620a3bff7cdd7a365be3376c97191aeaccc2a603e600951e452615bf89"
 name = "mmv"
 version = "1.0.0"
 dependencies = [
+ "getopt",
  "itertools",
  "tempfile",
 ]