Add day one solution.

day1_1.cr

@@ -0,0 +1,3 @@
+puts File.read("day1").split("\n")
+  .map(&.to_i)
+  .sum

day1_2.cr

@@ -0,0 +1,19 @@
+count = { 0 => 1 }
+acc = 0
+changes = File.read("day1").split("\n")
+  .select { |it| !it.empty? } 
+  .map(&.to_i)
+
+while true
+  changes.each do |i|
+    acc += i
+    old_count = count[acc]? || 0
+    new_count = old_count + 1
+    count[acc] = new_count
+
+    if new_count == 2
+      puts acc
+      exit
+    end
+  end
+end