jfiles: component file definitions

main functions:

  jappend
  jcreate
  jdup
  jerase
  jread
  jreplace
  jsize

  jopen
  jclose
  jseqno

  [0]   v  version
  [1]   s  starting component
  [2]   c  number of components
  [3]   l  file length
  [4]   d  directory pointer
  [5]   f  freelist pointer
  [6]   q  sequence number

  _1   file not found
  _2   invalid component
  _3   invalid data
  _4   host access error

Name	Type	Description
jappend	verb	append to jfile, (<i.2 3) jappend 'dat'
jcreate	verb	create jfile, jcreate 'dat'
jdup	verb	duplicate jfile, 'new' jdup 'dat'
jerase	verb	erase jfile, jerase 'dat'
jread	verb	read jfile, jread 'dat';2
jreplace	verb	replace in jfile, ('new value';123) jreplace 'dat';2 5
jsize	verb	return size of jfile, jsize 'dat'