Removed PDF conversion and all file input/output

All of textplay's previously built-in file input and output
functionality, and conversion (via 3rd party) to PDF, can be
accomplished using standard Unix redirects on the command-line.
Reproducing this inside textplay itself was cumbersome and unnecessary.
Textplay will remain a more Unix-like tool.
Bugfixes for empty line requirements after sluglines and dialogue
Notes are ignored when looking for empty lines around dialogue, scene
headings
Added makefile, updated documentation