fix: parse integer fields as base 10

toInt and toUint passed base 0 to strconv, which infers the base from the
literal the way the Go compiler does. A zero-padded CSV field was then
read as octal: 08 and 09 failed with invalid syntax and 010 silently
parsed as 8.

Pass base 10 at both call sites. Go-style prefixed literals such as 0x1f
are no longer accepted; they were undocumented and untested, and cannot
be kept without keeping the octal reading of 010 as well.

Closes #182

types.go

@@ -130,7 +130,8 @@ func toInt(in interface{}) (int64, error) {
 			return 0, nil
 		}
 		out := strings.SplitN(s, ".", 2)
-		return strconv.ParseInt(out[0], 0, 64)
+		// base 10, not 0: a CSV field is data, not a Go literal
+		return strconv.ParseInt(out[0], 10, 64)
 	case reflect.Bool:
 		if inValue.Bool() {
 			return 1, nil
@@ -164,7 +165,8 @@ func toUint(in interface{}) (uint64, error) {
 			}
 			return uint64(f), nil
 		}
-		return strconv.ParseUint(s, 0, 64)
+		// base 10, see toInt
+		return strconv.ParseUint(s, 10, 64)
 	case reflect.Bool:
 		if inValue.Bool() {
 			return 1, nil