Completed degree, radian, gradian builtin conversions

Updated CHANGES.

Updated help/unexpected.

Added help files for d2g(), d2r(), g2d(), g2r(), r2d(), r2g().

Added regression test code for the same functions.

Fixed a few minor typos.

help/r2d

@@ -0,0 +1,57 @@
+NAME
+    r2d - convert radians to degrees
+
+SYNOPSIS
+    r2d(x [,eps])
+
+TYPES
+    x		number (real or complex)
+    eps		nonzero real, defaults to epsilon()
+
+    return	number
+
+DESCRIPTION
+    Given x radians, return the equivalent number of degrees.
+
+    The eps controls the precision of the calculated internal
+    constant pi / 180.
+
+EXAMPLE
+    ; pi = pi(1e-20)
+    ; print r2d(pi), r2d(pi/3), r2d(2*pi)
+    180 60 360
+
+    ; print r2d(pi+4i), r2d(pi/3 + 1i*pi), r2d(pi/5 + 5i*pi)
+    180+~229.18311805232928350739i 60+180, 36+900i
+
+LIMITS
+    eps > 0
+
+LINK LIBRARY
+    NUMBER *qpidiv180(NUMBER *eps)
+
+SEE ALSO
+    d2r, g2r, r2g, d2g, g2d,
+    sin, cos, tan, sec, csc, cot, epsilon
+
+## Copyright (C) 2021  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:	2021/09/07 12:04:28
+## File existed as early as:	2021
+##
+## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
+## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/