Namespaces, function-pointers and bug fixes

- Fixed bug in optimizer
- Fixed `invalid types` messages in assignment into a constant
- Fixed saving strings into the verbal bytecode
- Fixed a small typo in `stdio.ss`
- Fixed parsing comments
- Fixed parsing function calls
- Improved command-line parameter reading
- Added a `label redeclaration` error
- Added namespace support (closes #8)
- Implemented function pointers (closes #4)
- Changed type-casting syntax (added operator `cast`)
- Many small improvements and fixes