PDF support more stable now

* Lays out cards with possiblity of margin, gap, and trim
* Some new directory and file validation
* Added a logger

samples/save_pdf.rb

@@ -0,0 +1,16 @@
+#!/usr/bin/env ruby
+require 'squib'
+
+Squib::Deck.new(width: 825, height: 1125, cards: 16) do
+  background color: :gray
+  rect x: 38, y: 38, width: 750, height: 1050, x_radius: 38, y_radius: 38
+
+  text str: (1..16).to_a, x: 220, y: 78, font: 'Arial 54'
+
+  save_pdf file: "sample-save-pdf.pdf", margin: 75, gap: 5, trim: 37
+
+  #Note that our PNGs still are not trimmed even though the pdf ones are
+  save_png range: 1, prefix: "save_pdf_"
+end
+
+puts "Done!"