Use https for Rubygems
Add dependencies needed to run yard
Simplify clean tasks

We don't really need to go through the ceremony of creating more
classes and methods.  We will always want to properly customize the
`clean` and `clobber` Rake tasks, so having this happen when the code
is required simplifies things.
Simplify s3 tasks

We don't really need to go through the ceremony of creating more
classes and methods.
Fix whitespace / formatting
Project documentation
Software documentation
Overrides documentation
Build Version documentation
Builder documentation
Fetcher documentation
Note on Config#install_dir
Add a place for custom exceptions
Pretty much rewrite top-level Omnibus + Config

This commit consolidates how Omnibus is configured.  Before, it
required both an omnibus.rb file AND additional undocumented
configuration in a Rakefile.

Now, the omnibus.rb file is completely unnecessary, along with much of
the Rakefile config.  Sane defaults are now in place, and most cases
can get by with simply adding

    Omnibus.configure

to the Rakefile.  If defaults need to be altered, just pass a block:

    Omnibus.configure do |config|
      ...
    end

Any places in existing project / software DSL files that refer to old
configuration parameters that were defined directly on the Omnibus
module will have to be change do refer to `Omnibus.config.$PARAMETER`.

Additionally, Rakefile configurations will need to be altered as well.
Move `project_root` and `source_root` up to main module.

Since these values cannot be changed/configured by the end-user it makes
more sense for them to live on the main `Omnibus` module.
Add a `Omnibus.root` -> `Omnibus.project_root` alias

This is mainly there for backward compatibility for legacy Omnibus
projects that use the older naming.
yarddoc format fixes
Add a `.yardopts` file and ignore generated `doc` dir
Add a Rakefile for bundler, rspec and yard tasks.
Add `Omnibus.omnibus_software_root` helper

This method is meant to act as the 'one true way' to retrieve the
location of the `omnibus-software` gem if it exists in the gem path. We
also find this using `Gem::Specification#find_all_by_name` which should
work in non-Bundler situations.