Flattened schema file names are too long

[jadams-tresys]

Apparently there are use cases where the flattened schema files need to be written to optical media but cannot have rock ridge extensions enabled, so filenames are limited to 64 characters and are truncated if longer. This obviously poses an issue with the flattened schemas and the naming convention of converting

/com/acme/xsd/schema.dfdl.xsd

to

com__acme__xsd__schema.dfdl.xsd

While preserving the directory layout is nice, we probably need to switch to using a hash for that portion of the filename or some other way of shortening the filenames.

[olabusayoT]

Possible solution could be to reduce the package names to 1 letter each ex c_a_x_schema.dfdl.xsd