Include an explicit note about the SWT dependency in the README

* making it clear so people know what to expect
* Help people resolve issues
* inspired through #954
Adjust the note about alpha/preview a bit
Moved SWT note to the other important notes not its own headline
Adding pry-nav to dev Gemfile

Often find this useful, so let's default it.
Adding rake console command
Fix for overlapping text

When flowing text to a second layout, we would stop short of consuming
all the vertical space provided us, but then position the second layout
based on the height of the first layout. Sometimes this resulted in
overlapping text.

Instead, we will now keep putting text into into the first layout until
it completely fills the height--even if it goes over by a little--so
that we get a smoother flow into the second layout.
Fix DSL parameters for star
Fix bounds checking on star
Use shoes-manual gem

This moves to relying on the shoes-manual gem for providing the manual
support. This includes getting the static files out of shoes-core, and
also moving the manual construction code to shoes-manual.
Add --manual option to main Shoes executable
Don't look for shoes-manual by path
Push packaging down to shoes-swt

Packaging was previously baked into the Shoes::CLI class, which lives up
in shoes. We don't want JRuby-specific dependencies at that level,
though, so this belonged down in shoes-swt.

We accomplish this by creating a DSL and backend class to represent
packaging, and call those from the CLI.
Merge pull request #955 from shoes/readme-adjustments

Readme adjustments
Specs. Do you run them?
Move CLI packaging spec to SWT
Merge pull request #959 from shoes/pry-nav

Add pry-nav and rake console to help with debugging
Merge pull request #960 from shoes/overlapping_text

Fix overlapping text with differing text heights

* fixes #942
* Changelog: improvement
Naming consistency and comments for star styles parameter
Move defaulting of values into Shoes::Star
Consistently use element_ for star bounds checking