gitignore: add _site/ to blacklist

Do not version control the generated website.

Signed-off-by: Michael Turquette <mturquette@deferred.io>
_includes: bootstrap: add submodule, v2.3.2

This is the first git submodule, so also creates .gitmodules.  Current
version is Twitter Bootstrap v2.3.2.

Signed-off-by: Michael Turquette <mturquette@deferred.io>
initial jekyll infrastructure

This commit introduces all of the bare essentials (as I see it) for a
nice Jekyll-generated website.  No frills here, and all content is
either generated from _includes/bootstrap via Liquid Template "include"
statements or it simply copied from the bootstrap sources.

There are no posts, only a single layout and index.html is the same
content found in bootstrap's "starter-template.html" example.

Check out the README.md for more info.

Signed-off-by: Michael Turquette <mturquette@deferred.io>