Added the `:alpha_char` syntax do make easier the definition of hashes. The `alpha_char` will be treated as a quoted string.
Improved the detection of the `lib` directory by `bin/sidef`; the absolute parent dir of sidef + 'lib' will be used as a library directory.
Added the alias `to_f` in `Convert` for converting strings to floating points. (the same as: `to_num`)
	new file:   scripts/Real-world problems/Converter/unit_converter.sf