Convert xwbtool to use GNU-style long options

[walbourn]

Embraces the -so vs. --long-option GNU-like pattern for the command-line tool.

This also adds -o=value which is the GNU standard and the tool already supported -o:value or -o value.

This is a hybrid of the Windows style and GNU-like pattern. For example, you can't combine single-characters together such as -yl with this tool like you can with GNU-style argument syntax. Not all multi-character options use -- which would be the GNU standard.

The tool already supports the -- escape so you can start filenames with / or -

[walbourn]

The help output for meshconvert now reads:

Microsoft (R) XACT-style Wave Bank Tool [DirectXTK] Version 000 (library)
Copyright (C) Microsoft Corp.
*** Debug build ***

Usage: xwbtool <options> [--] <wav-files>

   -r                  wildcard filename search is recursive
   -flist <filename>, --file-list <filename>
                       use text file with a list of input files (one per line)

   -s, --streaming          creates a streaming wave bank,
                            otherwise an in-memory bank is created
   -af, --advanced-format   for streaming, use 4K instead of 2K alignment
                            (required for advanced format drives without 512e)

   -o <filename>            output filename
   -h <h-filename>          output C/C++ header
   -l, --to-lowercase       force output filename to lower case
   -y, --overwrite          overwrite existing output file (if any)

   -c, --compact            force creation of compact wavebank
   -nc, --no-compact        force creation of non-compact wavebank
   -f, --friendly-names     include entry friendly names
   -nologo                  suppress copyright message

   '-- ' is needed if any input filepath starts with the '-' or '/' character

[walbourn]

walbourn/directxtktest#58