Eng 6265 add format currency func

Add a SQL function, FORMAT_CURRENCY. Its function is return a string in xx,xxx,xxx.xx format given a number. 
Please add test cases that operate on powers of 10 from 6 to -3, positive and negative: 1000000, 100000... 1, 0.1, .01, .001, -.001 -.01, -0.1, -1, -10 ... -1000000. 
Consider doing this in a loop to save lines of code -- you can put the expected values in a vector of strings.
Also test 0.