Silence "all" rules in Makefile
Introduce two helper operators to make code easier to write and read
Remove redundant parentheses
Annotate function with the exercise number that described it
Use interpreter in main functions
Disable MLton and enable SMLNJ in Makefile

SMLNJ takes less to compile and run the files I'm playing with, which
is a nice feature to have when developing.

MLton can be used when actually releasing software for production.
Annotate function with the exercise number that described it
Create structure representing a naive binary search tree
Extend tree to map keys to values and define a lookup function