Remove parent dir from lib_dirs for rebar.config

This is not needed to build neotoma and can cause build problems
depending on sibling directories of the checkout of neotoma.
Determine priv dir when in escript context using escript:script_name

When neotoma is escript-ized, use escript:script_name to determine the
location of neotoma's priv dir and peg_includes.hrl file. Using
code:priv_dir or code:where_is_file in escript context give
incorrect/difficult to interpret results.
Merge pull request #23 from seth/sf/script_name

Fix use of neotoma as an escript