bipack: auto-detect unsigned inline types and add @Varint field codec

docs/bipack.md

@@ -17,7 +17,7 @@ Bipack is a common kotlinx serializer that works pretty much like any other `kot
 - [BipackEncoder] to serializes anything to bipack format.
 - [BipackDecoder] deserializes from bipack back.
 
-There are also special annotation to fine tune the format: [Extendable], [Framed], [CrcProtected] for classes and [Unsigned] for integer data fields.
+There are also special annotation to fine tune the format: [Extendable], [Framed], [CrcProtected] for classes and [Unsigned], [Varint] for integer data fields.
 
 # Package net.sergeych.bintools
 
@@ -29,4 +29,4 @@ In particular, see [Varint] and [Smartint] variable-length compact integer codec
 
 To write a code that compiles and runs, and most likely works on the
 JS, native, and JVM, we need some portable/compatible synchronization 
-primitives. This package is a collection of such.
+primitives. This package is a collection of such.