Preprocessor outputs one sentence per line

Rather than having each word/tag tuple on a line, now each sentence is
on a single line
A few errors slip by and are printed on new lines, but it shouldn't be a
big issue

Also added preprocessor to makefile, syntax is:
	`make pre OUT=data/convert NUM=4`
OUT is the output directory and NUM is the number of merged output files
you want

closes #10