INT 21 - DOS 2+ - "FINDFIRST" - FIND FIRST MATCHING FILE
        AH = 4Eh
        AL = special flag for use by APPEND (see note below)
        CX = file attribute mask (see AX=4301h) (bits 0 and 5 ignored)
        DS:DX -> ASCIZ file specification (may include path and wildcards)
Return: CF clear if successful
            [DTA] = FindFirst data block (see below)
        CF set on error
            AX = error code (02h,03h,12h) (see AH=59h)
Notes:  for search attributes other than 08h, all files with at MOST the
          specified combination of hidden, system, and directory attributes
          will be returned.  Under DOS 2.x, searching for attribute 08h
          (volume label) will also return normal files, while under DOS 3+
          only the volume label (if any) will be returned.
        this call also returns successfully if given the name of a character
          device without wildcards.  DOS 2.x returns attribute 00h, size 0,
          and the current date and time.  DOS 3+ returns attribute 40h and the
          current date and time.
        immediately after an INT 2F/AX=B711h (APPEND return found name), the
          name at DS:DX will be overwritten; if AL=00h on entry, the actual
          found pathname will be stored, otherwise, the actual found path
          will be prepended to the original filespec without a path.
        under LANtastic, this call may be used to obtain a list of a server's
          shared resources by searching for "\\SERVER\*.*"; a list of printer
          resources may be obtained by searching for "\\SERVER\@*.*"
        under the FlashTek X-32 DOS extender, the filespec pointer is in DS:EDX
BUG:    under DOS 3.x and 4.x, the second and subsequent calls to this function
          with a character device name (no wildcards) and search attributes
          which include the volume-label bit (08h) will fail unless there is
          an intervening DOS call which implicitly or explicity performs a
          directory search without the volume-label bit.  Such implicit
          searches are performed by CREATE (AH=3Ch), OPEN (AH=3Dh), UNLINK
          (AH=41h), and RENAME (AH=56h)
SeeAlso: AH=4Fh,AX=4301h,INT 2F/AX=111Bh,INT 2F/AX=B711h

Format of FindFirst data block:
Offset  Size    Description
---PCDOS 3.10, PCDOS 4.01, MSDOS 3.2/3.3/5.0---
 00h    BYTE    drive letter (bits 0-6), remote if bit 7 set
 01h 11 BYTEs   search template
 0Ch    BYTE    search attributes
---DOS 2.x (and some DOS 3.x???)---
 00h    BYTE    search attributes
 01h    BYTE    drive letter
 02h 11 BYTEs   search template
---WILDUNIX.COM---
 00h 12 BYTEs   15-character wildcard search pattern and drive letter (packed)
 0Ch    BYTE    search attributes
---DOS 2.x and most 3.x---
 0Dh    WORD    entry count within directory
 0Fh    DWORD   pointer to DTA???
 13h    WORD    cluster number of start of parent directory
---PCDOS 4.01, MSDOS 3.2/3.3/5.0---
 0Dh    WORD    entry count within directory
 0Fh    WORD    cluster number of start of parent directory
 11h  4 BYTEs   reserved
---all versions, documented fields---
 15h    BYTE    attribute of file found
 16h    WORD    file time
                    bits 11-15: hour
                    bits 5-10:  minute
                    bits 0-4:   seconds/2
 18h    WORD    file date
                    bits 9-15:  year-1980
                    bits 5-8:   month
                    bits 0-4:   day
 1Ah    DWORD   file size
 1Eh 13 BYTEs   ASCIZ filename+extension