Add Shoes::App#quit
Add Shoes::App#quit

This method is necessary for testing the Qt backend.

This commit also disposes the Swt::Widgets::Shell object instead of the
display when quitting.
Add a tiny game "Pong in Shoes" (sample19) and revise Shoes::Swt::Common::{Painter, Fill, Stroke} a little bit.
Add app registration

Allows for nesting of apps. The app created by the first (outermost) app
block is the "main app". When this app's window is closed, the whole app
quits. Nested apps are not "main apps", and the main app continues to
run when nested apps are closed.
Add specs for app registration
Fixing OS X App name to display app title instead of SWT
Remove debugging
Tag Qt specs
Merge pull request #132 from wasnotrice/quit

We can have multiple apps.
Merge pull request #133 from kelcecil/mac-menubar-title

Fixing OS X App name to display app title instead of SWT
Changed #133 to JRuby-style camel case and specced it
In order to run sample4.rb, implement direct positioning on instantiation for TextBlock and add :text style for EditLine and EditBox.
Fixed #134.
Improved Button. When a button is clicked, the block is handed `self`. Try out sample7.rb.
Add Shoes::DIR. Refer to #105 and #107. Try out sample6.rb.
Fixed a bug. Now the following snippet works again.

Shoes.app do
  20.times{para 'hello'}
end
Fixed a bug. Try to run the following snippet and resize the window.

Shoes.app do
  stack do
    background green
    button 'hello'
    para 'hello ' * 20
    button 'hello'
  end
end
Fixed a few bugs. Try out sample 8, 9, 19 and the following snippet.

Shoes.app do
  f1 = stack width: 0.4 do
    background green
    para 'hello ' * 20
  end
  f2 = flow width: 0.6 do
    background yellow
    para 'shoes ' * 20
  end
  button 'debug' do
    p f1.contents.map(&:class)
    p f2.contents.map(&:class)
    p top_slot.contents.map(&:class)
    p [f1.left, f1.top, f1.width, f1.height]
    p [f2.left, f2.top, f2.width, f2.height]
  end
end
Fixed a bug. Try out the following snippet. The "hello" should be black.

Shoes.app do
  border red
  para 'hello'
end
Revised border, rect and oval. All borders paint a line around the inside of a slot, not the outside. Also rects and ovals are the same. Try out the following snippet.

Shoes.app do
  border green, curve: 50, strokewidth: 20
  rect 100, 100, 100, 100, fill: nil
  rect 200, 100, 100, 100, fill: nil
  rect 200, 200, 100, 100, fill: nil, strokewidth: 20
  oval 100, 200, 100, fill: yellow, stroke: red, strokewidth: 20
end