Auto-generated distinct macros per lib. Resolves #428

[iboB]

This was generated by the following ruby script:

SDECL = 'SOKOL_API_DECL'

def process_file(fname)
  lines = File.readlines(fname)

  lines.find { |line|
    line =~ /^#if.* SOKOL_([A-Z]_+)_INCLUDED/
  }
  ldecl = "SOKOL_#{$1}_API_DECL"

  decl_line = lines.index { |line|
    line =~ /^#if.* #{SDECL}/
  }

  return if !decl_line

  lines.map! { |line|
    line.
      gsub("#{SDECL}" + ' ' * (ldecl.length - SDECL.length), ldecl).
      gsub(SDECL, ldecl)
  }

  lines[decl_line, 0] = <<~EOF
    #if defined(#{SDECL}) && !defined(#{ldecl})
        #define #{ldecl} #{SDECL}
    #endif

  EOF

  File.write(fname, lines.join)
end

# process_file 'sokol_time.h'

Dir['**/*.h'].each do |f|
  process_file f
end

[iboB]

oops... forgot to mark this as a draft. Sorry about that

This is not ready to merge, yet. I saw some problems from the script. If all checks pass, I'll fix the problems manually

[iboB]

Ok. All checks have passed. I fixed the bad auto-generation of sokol_gfx_imgui.

@floooh I think this is ready for merge

[floooh]

Ok, I'm merging this now (manually, as I usually do). I wonder if the macro is actually needed inside the SOKOL_IMPL block too, I'll experiment with this on Windows a bit. (ah nvm, I confused this with the separate SOKOL_API_IMPL macro...), it'll probably make sense to give this the same treatment... I'll think about it.

[floooh]

..and merged, many thanks!