Revert "restore backwards compatibility after changes for Frege#165"

This reverts commit 3f59987.

Starting point for release 23

Updated copyright year

Start of work on 3.22

make final compiler in 3 stages

remove warnings

inline native constants

Make 'stdin', 'stdout' and 'stderr' thread local.

NOTE: Because the java type of those items changed from
PrintWriter/BufferedReader to ThreadLocal<PrintWriter>/ThreadLocal<BufferedReader>
this change is binary backwards compatible. In particular,
code compiled with an earlier version will try to access
'stdout' as 'PrintWriter'.

Inserted reference to Language.pdf

fix Issue#61