Add initial JSON formatter

It works and can format all "plain" Perl data, but has a few known bugs
and limitations that still need to be worked out.

It's about 8x smaller than JSON::XS's encoder and *much* smaller than
Cpanel::JSON::XS, but this is just a first attempt, it'll grow.

FU.pod

@@ -0,0 +1,13 @@
+=head1 NAME
+
+FU - A collection of awesome modules plus a lean and efficient web framework.
+
+=head1 SYNOPSIS
+
+=head1 DESCRIPTION
+
+=head2 Properties
+
+- Requires a moderately recent Perl (>= 5.36).
+- Only works on 64-bit Linux (and possibly *BSD).
+- Assumes that no threading is used; not all modules are thread-safe.