RAA - pascal-tri

This library (though not quite in library form yet) creates a class which allows you to grab an almost-arbitrary row from a Pascal like triangle.

Features:
- includes a function to pretty-print the triangle up to a specified row
- you can pass a Proc to define how the class creates a new value from the two seed/parent values on the previous row
- you can pass a Proc to define how the class creates outer values
- you can pass the initial value
- creates rows of the traditional Pascal's triangle when no args are passed to #initialize

Current limitations (to be fixed soon):
- floating-point values aren't formatted correctly
- doesn't allow you to use different numbers for the right outside and left outside

Previous limitations (fixed in current release):
0.1:
- used a completely recursive method of creating new rows (so the number of new rows that could be created at once was limited by the stack)