Resolves #256 by adding DXT support to the stdio module in the model of POSIX's DXT support. Specifically it supports Lustre module integration (when compiled) and attempts to store offsets using the existing mechanism implemented in stdio_file_record_ref.

A cursory test suggests that both DXT and darshan-dxt-parser work on a non-MPI Python application, but this MR needs more thorough testing. Specifically, correctness should be tested under the following conditions:

• a well-defined workload that includes
  • fscanf
  • fgetc/fgets/fputc/fputs/getw/putw
  • printf/fprintf
  • fflush
  • rewind/fseek/fseeko/fsetpos
• with MPI case
• with multiple threads
• compatibility with other darshan-dxt-parser and darshan-parser versions - I wasn't sure how to handle STDIO-DXT-specific versioning inside the DXT module

Was a test ever created for the original stdio module implementation that we can repurpose?