Support calling BAM pack via 'python -m bam.pack'.

This allows us to run "setup.py bdist_wheel", put the wheel on the
PYTHONPATH, and run BAM pack without having to install it on a virtualenv.
The main purpose is to be able to ship this wheel with Blender. Updating
Blender's version of BAM thus requires only putting in a new wheel file,
rather than the old error-prone approach of copy-and-edit.

bam/__main__.py

@@ -0,0 +1,8 @@
+"""Main module for running python -m bam.
+
+Doesn't do much, except for printing general usage information.
+"""
+
+print("The 'bam' module cannot be run directly. The following subcommand is available:")
+print()
+print("python -m bam.pack")

bam/pack.py

@@ -0,0 +1,10 @@
+"""CLI interface to BAM-pack.
+
+Run this using:
+
+python -m bam.pack
+"""
+
+if __name__ == '__main__':
+    from bam.blend import blendfile_pack
+    blendfile_pack.main()