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/acoversin

@@ -11,11 +11,10 @@ TYPES
     return	number
 
 DESCRIPTION
-    Calculate the inverse coversed sine of x to a multiple of eps with error less in
+    Calculate the inverse coversed trigonometric sine of x to a multiple of eps with error less in
     absolute value than .75 * eps.
 
-    The coversed sine function is sometimes called covers, or acosiv, or acvs,
-    may be defined as:
+    This function is sometimes called acovers, or acvs, or arccoversin, is equivalent to:
 
 	acoversin(x) = asin(1 - x)
 
@@ -36,8 +35,8 @@ LINK LIBRARY
 SEE ALSO
     sin, cos, tan, cot, sec, csc
     asin, acos, atan, acot, asec, acsc
-    versin, coversin
-    aversin
+    versin, coversin, vercos, avercos
+    aversin, acoversin, covercos, acovercos
     epsilon
 
 ## Copyright (C) 2023  Landon Curt Noll