bin/build is now built from pre-commit hook (fatten -o build build.lean)

Closes #37

Complete pre-commit hook below.

```
use 5.010;
use strict;
use warnings;
use autodie qw(:all);
use FindBin qw($Bin);
use Cwd;

chdir("$Bin/../../bin");

system("fatten --quiet -i build.lean -o build 2> ../.fatten.out");

system(qw( chmod +x build ) );

chdir("$Bin/../..");

system(qw( git --git-dir=.git add bin/build ));

exit 0;
```