add two new writers: a dummy "none" writer that disables output and a "stats" writer that outputs general info only about token counts and annotation info

initial switch to use shared_ptrs for sentence and chunk objects, ale get rid of the pointless sentence template

Libcorpus2 now contains the base strructures (tokens etc), their I/O and related classes.
Libpwrutils (name TBD) contains basic building blocks common to all tagger-related libraries
Tagset-tool only needs libcorpus, so was brough here as well.