OptionalKeywords: Syntax of HicEst functions with optional arguments (keywords)

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function with optional argument(s):
- function( [keyword1 [= type1]] [..., keywordN [= typeN]] )
HicEst knows 2 kinds of functions with optional keywords:
- Keyword order is irrelevant: each keyword should occur only once
  - OPEN(FIle="text.txt", NEW) ! 1 file only in an OPEN statement
- Multiple occurences are allowed: keywords are executed in the given order
  - DLG(Edit=num, Edit=string, Button="OK", Button="Cancel")
Use VARIABLES if a return value is needed:
- DLG(..., X0=lastX) ! return the x position in the VARIABLE lastX
Minimum keyword characters are given in UPPERCASE. Include lowercase letters to
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, e.g.:
- "RPL" or "rpl" or "replby" are all valid short forms of the optional keyword "RePLaceby",
- "rep" generates an error message (the letter "L" is missing),
- "RLP" is invalid (wrong order of letters).
- Expressions are evaluated BEFORE the keywords are worked off:
  - EDIT(.. , GetPosition=i, .., SetPosition=i+5,..)
  - ! the value of i+5 is evaluated BEFORE the option Get=i is executed

type	meaning of type	example keyword	example
NUM	numeric VARIABLE required	WINdowhandle =	win=wh
num	numeric argument required	Height =	H=20
[=NUM]	optional num arg (default is n)	Line =	L=3
txt	character argument required	TeXt =	tx="abc"
TXT	character VARIABLE required	TeXt =	tx=Name
[O]	optional char arg (default is "O")	Message =	m="?Y2"
n/c	numeric OR character required	Edit =	e=string
log	num arg required, TRUE if not 0	UnderLine =	ul= i<3
[T]	TRUE if keyword is present	APPend	app
LBL	on error jump to label	ERror =	er=999
vec	vector argument (no subscripts)	GetPosition =	gp=PosVec
NxM	numeric matrix as argument	Matrix =	m=mtx
arr	vector OR matrix as argument	Transpose =	t=mtx
xpr	expression to evaluate	NUL =	NUL=COS(x)
SUB	subroutine name to be called	CallBack =	cb=sub
---	no argument	Mark1	m1

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