Updates and Fixes

**resource.go/assets.go**
*  renamed `resources.go` to `assets.go`
*  added dark glyphs - located in assets.go -> assets/glyphs/dark/
*  moved original glyphs - located in assets.go -> assets/glyph/light/

**glyphbanner.go**
* added option to make glyphs vertical and/or dark

**rpcg.go**
* Added a random portal code generator this function takes no args and returns a string

**README.md**
* Fixed some typos (probably more to be fixed)
* Added example of vertical portal banner
* Added list of options for banner creation
* Added example of ``nmslib.RndPortal()`` usage

**go.mod**
* updated go version to 1.16

convert.go

@@ -8,11 +8,8 @@ import (
 )
 
 /*
-	The maths are all thanks to:
-	Xainesworld
-		- YT Channel - https://www.youtube.com/channel/UCzTB8EBVJWkzJi2sQjdBv9g
-		- Video: https://www.youtube.com/watch?v=xmZbkTahw4w
-		- Website: https://www.xainesworld.com/
+	Xainesworld	Video: https://www.youtube.com/watch?v=xmZbkTahw4w
+	Fandom Wiki: https://nomanssky.fandom.com/wiki/Portal_address
 */
 
 /*
@@ -63,7 +60,7 @@ func P2gc(p string) (gc string, err error) {
 		gc = fmt.Sprintf("%04X:%04X:%04X:%04X", coord[3], coord[1], coord[2], coord[0])
 
 	} else { // if len(p) != 12 return an error
-		return "", errors.New("A 12char HEX string is required. example: 006afa556c30")
+		return "", errors.New("a 12char HEX string is required. example: 006afa556c30")
 	}
 	return // return formated string
 }