Break util.cr into multiple files

src/util/numeric_sort.cr

@@ -0,0 +1,40 @@
+# Properly sort alphanumeric strings
+# Used to sort the images files inside the archives
+# https://github.com/hkalexling/Mango/issues/12
+
+def is_numeric(str)
+  /^\d+/.match(str) != nil
+end
+
+def split_by_alphanumeric(str)
+  arr = [] of String
+  str.scan(/([^\d\n\r]*)(\d*)([^\d\n\r]*)/) do |match|
+    arr += match.captures.select { |s| s != "" }
+  end
+  arr
+end
+
+def compare_numerically(c, d)
+  is_c_bigger = c.size <=> d.size
+  if c.size > d.size
+    d += [nil] * (c.size - d.size)
+  elsif c.size < d.size
+    c += [nil] * (d.size - c.size)
+  end
+  c.zip(d) do |a, b|
+    return -1 if a.nil?
+    return 1 if b.nil?
+    if is_numeric(a) && is_numeric(b)
+      compare = a.to_big_i <=> b.to_big_i
+      return compare if compare != 0
+    else
+      compare = a <=> b
+      return compare if compare != 0
+    end
+  end
+  is_c_bigger
+end
+
+def compare_numerically(a : String, b : String)
+  compare_numerically split_by_alphanumeric(a), split_by_alphanumeric(b)
+end