Include string encoding in string_t.

[cparser] / lextest / tokenstreams / refresults / numbers

'newline'
integer number 0
'newline'
integer number 1
'newline'
integer number 12
'newline'
integer number 42
'newline'
integer number 12345
'newline'
integer number 123456789
'newline'
integer number 1
'newline'
integer number 66
'newline'
integer number 255
'newline'
integer number 83
'newline'
integer number 83
'newline'
floatingpointer number 1234567890000000000.000000
'newline'
'newline'
end of file