add vercos(), avercos(), covercos(), acovercos()

Improved trig help files.

Added new vercos(x, [,eps]) for versed cosine and covercos(x, [,eps])
for inverse versed cosine.

Added new avercos(x, [,eps]) for inverse versed cosine and acovercos(x, [,eps])
for inverse coversed cosine.

help/vercos

@@ -0,0 +1,69 @@
+NAME
+    vercos - versed trigonometric cosine
+
+SYNOPSIS
+    vercos(x [,eps])
+
+TYPES
+    x		number (real or complex)
+    eps		0 < real < 1, defaults to epsilon()
+
+    return	number
+
+DESCRIPTION
+    Calculate the versed trigonometric cosine of x to a multiple of eps with error less in
+    absolute value than .75 * eps.
+
+    This function is sometimes called verc, is equivalent to:
+
+	vercos(x) = 1 + cos(x)
+
+EXAMPLE
+    ; print vercos(0.2), vercos(3/7), vercos(-31)
+    1.98006657784124163112 1.90956035167416667403 1.91474235780453127896
+
+    ; print vercos(1, 1e-5), vercos(1, 1e-10), vercos(1, 1e-15), vercos(1, 1e-20)
+    1.5403 1.5403023059 1.54030230586814 1.5403023058681397174
+
+    ; print vercos(2 + 3i, 1e-5), vercos(2 + 3i, 1e-10)
+    -3.18963-9.10923i -3.189625691-9.1092278938i
+
+    ; pi = pi(1e-20)
+    ; print vercos(pi/3, 1e-10), vercos(pi/2, 1e-10), vercos(pi, 1e-10), vercos(3*pi/2, 1e-10)
+    1.5 1 0 1
+
+LIMITS
+    0 < eps < 1
+
+LINK LIBRARY
+    NUMBER *qvercos(NUMBER *x, NUMBER *eps)
+    COMPLEX *c_vercos(COMPLEX *x, NUMBER *eps)
+
+SEE ALSO
+    sin, cos, tan, cot, sec, csc
+    asin, acos, atan, acot, asec, acsc
+    versin, coversin, vercos, avercos
+    aversin, acoversin, covercos, acovercos
+    epsilon
+
+## Copyright (C) 2023  Landon Curt Noll
+##
+## Calc is open software; you can redistribute it and/or modify it under
+## the terms of the version 2.1 of the GNU Lesser General Public License
+## as published by the Free Software Foundation.
+##
+## Calc is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
+## Public License for more details.
+##
+## A copy of version 2.1 of the GNU Lesser General Public License is
+## distributed with calc under the filename COPYING-LGPL.  You should have
+## received a copy with calc; if not, write to Free Software Foundation, Inc.
+## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+##
+## Under source code control:	2023/09/05 23:25:28
+## File existed as early as:	2023
+##
+## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
+## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/