Finished DigitalSky.java and TopMSloan.java.

These will be used to compare the Haskell priority queues with the java
binary heap implementation as given in Sedgewick.

new file:   .gitignore
new file:   DigitalSky.java
modified:   LeftistHeap.hs
new file:   TopM.java
new file:   TopMSloan.java
new file:   Transaction.java
new file:   algs4.jar
new file:   sdssSmall.csv
new file:   stdlib.jar