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/covercos

@@ -0,0 +1,69 @@
+NAME
+    covercos - coversed trigonometric cosine
+
+SYNOPSIS
+    covercos(x [,eps])
+
+TYPES
+    x		number (real or complex)
+    eps		0 < real < 1, defaults to epsilon()
+
+    return	number
+
+DESCRIPTION
+    Calculate the coversed trigonometric cosine of x to a multiple of eps with error less in
+    absolute value than .75 * eps.
+
+    This function is sometimes called cvc, is equivalent to:
+
+	covercos(x) = 1 + sin(x)
+
+EXAMPLE
+    ; print covercos(0.2), covercos(3/7), covercos(-31)
+    1.19866933079506121546 1.41557185499305200807 1.40403764532306500605
+
+    ; print covercos(1, 1e-5), covercos(1, 1e-10), covercos(1, 1e-15), covercos(1, 1e-20)
+    1.84147 1.8414709848 1.841470984807896 1.84147098480789650665
+
+    ; print covercos(2 + 3i, 1e-5), covercos(2 + 3i, 1e-10)
+    10.1545-4.16891i 10.1544991469-4.16890696i
+
+    ; pi = pi(1e-20)
+    ; print covercos(pi/6, 1e-10), covercos(pi/2, 1e-10), covercos(pi, 1e-10), covercos(3*pi/2, 1e-10)
+    1.5 2 1 0
+
+LIMITS
+    0 < eps < 1
+
+LINK LIBRARY
+    NUMBER *qcovercos(NUMBER *x, NUMBER *eps)
+    COMPLEX *c_covercos(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 23:31:08
+## 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/