release 1.8

• script fixes
• updated kotlin sdk version
• many code cleanups and improvements
• added code optimization: removal of unused code and variables, subroutine inlining
• added travis CI builds
• added AST-based virtual machine (-avm command line option) it runs on the internal AST directly, without needing byte codes
• strlen functions now terminate at the first zero byte
• better implicit type casting
• the stackvm and astvm can now print in different colors