Fix Shebang Error

The previous shebang "/usr/bin/node" would throw error if user
has NOT installed Node.js on at the path. Using "/usr/bin/env"
would allow finding Node.js wherever it is installed.

The file is also renamed and made executable for easier invocations
from inside the modules directory. For example, to invoke the
script from  a project having installed the module would simply run
"./node_modules/tableify/bin/tableify"