Fix paths

make file was forgotne when 'dlex' package was created
Remove usage of map&join

For some reason, toString was called twice per children.
This caused number of function calls grow exponentialy for nested structures
Add '.' support & flatten ast.Or()

'.' matches any character (actualy it matches any 'char' from 0x00 to 0xFF)

Since '.' includes also invalid unicode characters,
ast.Letter.toString was improved to show hex representation for non-ascii characters