Improve error message for LEX_003
Fix inconsistencies in error positions
Improve error message for LEX_004
Improve error message for LEX_005
Improve error message for LEX_006
Improve error messages for LEX_007 and LEX_008
Improve error message for LEX_011
Improve error message for LEX_012
Improve error message for LEX_013
Improve error message for LEX_014
Improve error message for LEX_015
Improve error message for LEX_017