Pages should render faster

Bumping the parallel gem
Running page rendering in seperate processes
Fixes Issue #435 (noisy)

Introduced a new debug flag (-D, --debug) which will log to the debug
log, and also the console.
The verbose flag now displays more info during the build, specifically
copying and generating of files.
Fixing issue #433 (awestruct env and env-site)

Adding the `env` and `env-site` attributes. `env-site` is set at true. `env` is
set at `@site`. The `awestruct` attributes, save `awestruct-version` are
now deprecated and will not be honored in a future version.
Fixes issue #426 (`site` from _ext/pipeline)

You can now access `site` from with _ext/pipeline simply by calling
site, which is now a private method of that class.
Fixes issue #383 (configurable tag cloud template)

The tag cloud extension now will take a `:template` as part of the
options. This must be a file path that `engine.load_page` can load and
use.

If no `:template` is given as part of the initialization the default,
which was being used all along, is used.
Fixing issue #434 (better yaml errors)

The standard errors that happen if there are problems during page
generation are now used for yaml loading errors. It will now tell you
the file that was being processed, and the error message along with
backtrace.

Also did some reformatting in the base_tilt_handler.
Fixing tests I broke