Add packager.py wrapper for Emscripten file_packager.py.

This tool can be used to package a single file or all files
from one directory and its subdirectories. It creates an html
file with the output of file_packager.py included, plus
an associated .data file. DOSBox can run the packaged program
with those two files plus dosbox.js.

This triggers Emscripten bug:
https://github.com/kripken/emscripten/issues/1992
A patch must be applied to the postamble to prevent DOSBox from
being run twice and failing.
Set up default compiler flags for usable result.

This disables -g because it creates huge JavaScript, which uses
huge amounts of memory in Firefox.

Memory is set to 64 MB. Previous testing was with 128, but 64
seems to be enough for the default DOSBox configuration.