:start :end nodes stored in independent maps

The entire parsed data structure is a map with three data members:
	* :start - this is possible start nodes, with frequencies
	* :end - this is the set of end nodes
	* :counts - this is the same count structure previously outlined
Reordering. Pushed markov into own namespace.

parser is the code which generates the parse structure; builder is the
code which actually uses the structure to construct the sentences. Well,
it will be, once I write it.