Removing the accessor in favor of #to_a

It made more sense to me to represent the Template object as an
array using the #to_a convention rather than giving access to the
internal storage mechanism via an accessor.
Updating README with some guesses

The way Clerk is used has changed drastically. This is a first
stab at getting the README updated to reflect the new Templating
which also led to some tweaks for the rest of the usage of Clerk.
The sections about how to use parsing will have to be fleshed out
elsewhere.