Convert meshconvert tool 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) MeshConvert Command-line Tool [DirectXMesh] Version 166 (library)
Copyright (C) Microsoft Corp.
*** Debug build ***

Usage: meshconvert <options> [--] <files>

   Input file type must be Wavefront Object (.obj)

   -ft <filetype>, --file-type <filetype>  output file type
       sdkmesh:  DirectX SDK .sdkmesh format (default)
       sdkmesh2: sdkmesh format version 2 (PBR materials)
       cmo:      Visual Studio Content Pipeline .cmo format
       vbo:      Vertex Buffer Object (.vbo) format
       obj:      WaveFront Object (.obj) format

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

   -n, --normal-by-angle   -na, --normal-by-area   -ne, --normal-by-equal
                                  generate normals weighted by angle/area/equal
   -t, --tangents                 generate tangents
   -tb, --tangent-frame           generate tangents & bi-tangents
   -cw, --clockwise               faces are clockwise (defaults to counter-clockwise)

   -op, --optimize   -oplru, --optimize-lru
                                  vertex cache optimize the mesh (implies -c)
   -c, --clean                    mesh cleaning including vertex dups for attribute sets
   -ta, --topological-adjacency -or- -ga, --geometric-adjacency
                                  generate topological vs. geometric adjacency (def: ta)

   -nodds                         prevents extension renaming in exported materials
   -flip, --flip-face-winding     reverse winding of faces
   --flip-u                       inverts the u texcoords
   --flip-v                       inverts the v texcoords
   --flip-z                       flips the handedness of the positions/normals
   -o <filename>                  output filename
   -l, --to-lowercase             force output filename to lower case
   -y, --overwrite                overwrite existing output file (if any)
   -nologo                        suppress copyright message

       (sdkmesh/sdkmesh2 only)
   -ib32, --index-buffer-32-bit   use 32-bit index buffer
   -fn <normal-format>, --normal-format <normal-format>
                                  format to use for writing normals/tangents/binormals
   -fuv <uv-format>, --uv-format <uv-format>
                                  format to use for texture coordinates
   -fc <color-format>, --color-format <color-format>
                                  format to use for writing colors

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

   <normal-format>: float3 float16_4 r11g11b10 

   <uv-format>: float2 float16_2 

   <color-format>: bgra rgba float4 float16_4 rgba_10 r11g11b10 

All the existing older switches are still accepted, but are deprecated per this table:

Old switch	New switch
-sdkmesh	-ft sdkmesh --file-type sdkmesh
-sdkmesh2	-ft sdkmesh2 --file-type sdkmesh2
-cmo	-ft cmo --file-type cmo
-vbo	-ft vbo --file-type vbo
-wf	-ft obj --file-type obj
-flipu	--flip-u
-flipv	--flip-v
-flipz	--flip-z

[walbourn]

https://github.com/walbourn/directxmeshtest/pull/21/files