Special constants

- Added a `special constants`:
-> `__selffunc`, string -> current function name, eg."main"
-> `__self`, string -> currently compiled file (absolute path)
-> `__compiler_version`, string -> string compiler version, eg."2.1"
-> `__compiler_iversion`, float -> compiler version, eg.`2.1`
-> `__line`, int -> current line
-> `__date`, string -> compilation date; format dd-mm-yyyy
-> `__time`, string -> compilation time; format hh:mm
-> They can be turned on by the `-sconst` switch
- Changed a bit `compile_all.bat`
- Finished `short_cast.ss`
- Small change in `readme.md`