add trigonometric chord of a unit circle functions

Improve builtin function strings, as printed by help builtin,
that use an optional accuracy (epsilon) arg by adding a comma.

Added the following new trigonometric functions:

    crd(x [,eps])		trigonometric chord of a unit circle
    acrd(x [,eps])		inverse trigonometric chord of a unit circle

help/Makefile

@@ -200,23 +200,24 @@ BLT_HELP_FILES= ${BLT_HELP_FILES_3} ${BLT_HELP_FILES_5} \
 # to keep this list in nice sorted order.
 #
 DETAIL_HELP= abs access acos acosh acot acoth acovercos acoversin \
-	acsc acsch address agd ahacovercos ahacoversin ahavercos ahaversin \
-	append appr arg argv arrow asec asech asin asinh assign atan atan2 \
-	atanh avercos aversin avg base base2 bernoulli bit blk blkcpy blkfree \
-	blocks bround btrunc calc_tty calclevel calcpath catalan ceil cfappr \
-	cfsim char cmdbuf cmp comb conj cos cosh cot coth count covercos \
-	coversin cp csc csch ctime d2dm d2dms d2g d2r delete den dereference \
-	det digit digits display dms2d dp epsilon errcount errmax errno error \
-	errsym estr euler eval exp fact factor fclose fcnt feof ferror fflush \
-	fgetc fgetfield fgetfile fgetline fgets fgetstr fib files floor fopen \
-	forall fpathopen fprintf fputc fputs fputstr frac free freebernoulli \
-	freeeuler freeglobals freeredc freestatics frem freopen fscan fscanf \
-	fseek fsize ftell g2d g2gm g2gms g2r gcd gcdrem gd getenv gms2g h2hm \
-	h2hms hacovercos hacoversin hash havercos haversin head highbit hmean \
-	hms2h hnrmod hypot ilog ilog10 ilog2 im indices inputlevel insert int \
-	inverse iroot isalnum isalpha isassoc isatty isblk iscntrl isconfig \
-	isdefined isdigit iserror iseven isfile isgraph ishash isident isint \
-	islist islower ismat ismult isnull isnum isobj isobjtype isodd isprime \
+	acrd acsc acsch address aexcsc aexsec agd ahacovercos ahacoversin \
+	ahavercos ahaversin append appr arg argv arrow asec asech asin asinh \
+	assign atan atan2 atanh avercos aversin avg base base2 bernoulli bit \
+	blk blkcpy blkfree blocks bround btrunc calc_tty calclevel calcpath \
+	catalan ceil cfappr cfsim char cmdbuf cmp comb conj cos cosh cot coth \
+	count covercos coversin cp crd csc csch ctime d2dm d2dms d2g d2r \
+	delete den dereference det digit digits display dms2d dp epsilon \
+	errcount errmax errno error errsym estr euler eval excsc exp exsec \
+	fact factor fclose fcnt feof ferror fflush fgetc fgetfield fgetfile \
+	fgetline fgets fgetstr fib files floor fopen forall fpathopen fprintf \
+	fputc fputs fputstr frac free freebernoulli freeeuler freeglobals \
+	freeredc freestatics frem freopen fscan fscanf fseek fsize ftell g2d \
+	g2gm g2gms g2r gcd gcdrem gd getenv gms2g h2hm h2hms hacovercos \
+	hacoversin hash havercos haversin head highbit hmean hms2h hnrmod \
+	hypot ilog ilog10 ilog2 im indices inputlevel insert int inverse iroot \
+	isalnum isalpha isassoc isatty isblk iscntrl isconfig isdefined \
+	isdigit iserror iseven isfile isgraph ishash isident isint islist \
+	islower ismat ismult isnull isnum isobj isobjtype isodd isprime \
 	isprint isptr ispunct isqrt isrand israndom isreal isrel issimple \
 	isspace issq isstr istype isupper isxdigit jacobi join lcm lcmfact \
 	lfactor ln log log2 logn lowbit ltol makelist matdim matfill matmax \