troffcvt Support for groff

troffcvt supports the following groff extensions to standard troff:

• Long names. Contexts in which long names are legal include:
  

     .xxx           Long request and macro names
     \[xxx]         Long special character names
     \*[xxx]        Long string names
     \n[xxx]        Long register names
     \f[xxx]        Long font names
     \$[nnn]        Long (>9) macro argument references
  

• Compatibility mode. The .cp request and .C register are supported. Compatibility may be turned on from the troffcvt command line with the -C option.
  
• The .mso request.
  
• The .do request.
  
• The \$* and \$@ macro argument references.
  
• The \$0 macro name reference.
  
• More than 9 macro arguments may be referenced (up to 99, though groff allows more). For macros above \$9, the notation \[nnn] may be used.
  
• Aliases (the .als and .aln requests).
  
• The .shift request.
  
• Named environments and the .ev string-valued register.
  
• The \A'xx' escape sequence.
  
• The .if d conditional test.
  
• The .if r conditional test.
  
• The .if c conditional test.