math/big: cleanup documentation for Format methods

'b' is a standard verb for floating point values. The runes like '+'
and '#' are called "flags" by package fmt's documentation. The flag
'-' controls left/right justification, not anything related to signs.

Change-Id: Ia9cf81b002df373f274ce635fe09b5bd0066aa1c
Reviewed-on: https://go-review.googlesource.com/20930Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/math/big/ftoa.go

@@ -374,12 +374,11 @@ func min(x, y int) int {
 }
 
 // Format implements fmt.Formatter. It accepts all the regular
-// formats for floating-point numbers ('e', 'E', 'f', 'F', 'g',
-// 'G') as well as 'b', 'p', and 'v'. See (*Float).Text for the
-// interpretation of 'b' and 'p'. The 'v' format is handled like
-// 'g'.
+// formats for floating-point numbers ('b', 'e', 'E', 'f', 'F',
+// 'g', 'G') as well as 'p' and 'v'. See (*Float).Text for the
+// interpretation of 'p'. The 'v' format is handled like 'g'.
 // Format also supports specification of the minimum precision
-// in digits, the output field width, as well as the format verbs
+// in digits, the output field width, as well as the format flags
 // '+' and ' ' for sign control, '0' for space or zero padding,
 // and '-' for left or right justification. See the fmt package
 // for details.

src/math/big/intconv.go

@@ -52,16 +52,16 @@ func writeMultiple(s fmt.State, text string, count int) {
 	}
 }
 
-// Format is a support routine for fmt.Formatter. It accepts
-// the formats 'b' (binary), 'o' (octal), 'd' (decimal), 'x'
-// (lowercase hexadecimal), and 'X' (uppercase hexadecimal).
+// Format implements fmt.Formatter. It accepts the formats
+// 'b' (binary), 'o' (octal), 'd' (decimal), 'x' (lowercase
+// hexadecimal), and 'X' (uppercase hexadecimal).
 // Also supported are the full suite of package fmt's format
-// verbs for integral types, including '+', '-', and ' '
-// for sign control, '#' for leading zero in octal and for
-// hexadecimal, a leading "0x" or "0X" for "%#x" and "%#X"
-// respectively, specification of minimum digits precision,
-// output field width, space or zero padding, and left or
-// right justification.
+// flags for integral types, including '+' and ' ' for sign
+// control, '#' for leading zero in octal and for hexadecimal,
+// a leading "0x" or "0X" for "%#x" and "%#X" respectively,
+// specification of minimum digits precision, output field
+// width, space or zero padding, and '-' for left or right
+// justification.
 //
 func (x *Int) Format(s fmt.State, ch rune) {
 	// determine base