SyntaxOk fixed as proposed partly by Helmut. Refs: #29.
Len replaced by LEN in DevSubTool.
Equal adapted for supporting 16-bit Unicode and simplified in DevLinkChk.
Subsystem syntax definition in Tut-3 synchronized with the implementation in the compiler and loader.
Error messages adapted.
In DevSubTool:
- the maximum subsystem prefix length is no longer checked
- the leading capital letter in the subsystem prefix is no longer checked

Signed-off-by: Josef Templ <josef.templ@gmail.com>