Tag body with a directive in it.

Implemented directives within tags where the directive is specified by
the invocation.

Closes #77.
Test subsequent generation of tag body.

Ensure that a tag body will be resolved when a regeneration fabricates a
directive body that includes a tag. The conditional must call `rewrite`
for the directives in the fabricated directive body with a generating
flag set to true.

Closes #79.
Remove `isDirective` constant.

The directive regular expression is only ever used once.
Spell check `README.md`.
Track frame.

Instead of using a frame context object, I'm using an array that
contains the state of the previous frame, where a frame is a descent
within a specific template. The use of a frame object to gather the
variables in the `rewrite` and directive handler function signatures
caused the source to grow by 0.8k instead of the 0.2k that comes from
adding the `frame` parameter to the `rewrite` function signature.
Layouts.

Implement layouts with named blocks.

Leaning toward using ECMA 5 and requesting that IE 8 users shim. It is
the right thing to do, to move everyone over to the new standards. IE 8
is the new IE 6, a laggard that requires special preprocessing, we
always have one Microsoft browser we're molly-coddling, so let it now be
IE 8, but don't let the molly-coddling ruin the code.

I realy only want to use `forEach` and `filter`, which might reduce to just
`filter`, and then there is only one function to shim. I'm going to work
with `forEach` and `filter`, then later I'll see how much the size
explodes when I shim `filter` or replace `filter` with `for` loops.

Closes #63.
Merge branch `tag` into `master`.