Add four new exercises

[ErikSchierboom]

This PR adds four new exercises:

1. beer-song
2. pascals-triangle
3. saddle-points
4. kindergarten-garden

These four exercises were all on the "left-to-implement" list as specified in issue #2.

[jwood803]

All looks good to me!

[ErikSchierboom]

@jwood803 Great! I'll be working on more exercises in the coming weeks, hopefully implementing every exercise listed in #2.

Once than is done, I'll port them to the F# track.

[kytrinyx]

Thanks, Erik! This is great.