Plugin infrastructure in corpus2 readers: plugin loading code in pwrnlp/plugin, chanegs all around to accomodate

turn on autodoc for some TokenWriter swig wrapper functions and add shared_ptr overloads for write_*

rename .i files in swig wrappers, correct dependendcies so touching any .i file will rebuild the wrappers

Revert "add has_more to readers". Not needed with the upgraded shared_ptr swig wrappers (and also not fully correct).

This reverts commit 99388c53.

add .get(), __bool__ and __nonzero__ to shared_ptr wrapper to allow testing if the shared_ptr is valid

(swig) Added corpus2 library. To use corpus2 python library (wrappers for C++ corpus2) you should do: 'import corpus2' in python

Handle exceptions thrown by create_stream_writer, create_path_writer, create_stream_reader, create_path_reader