add a gitignore file
first commit of erlkm_node, the workhorse data structure module that represents a "node" in the canonical kohonen map.
added add/2, subtract/2, scale/2 implementations for simple euclidian vectors.
we also need the concepts of addition, subtraction, and scalar multiplication.
updating formula is D' = D + P*(D - S), in which i had forgotten the addition of D on the RHS.