Clean up option parsing and identifier quoting in Producer::PostgreSQL

Remove the unused quote_field_names and table_name options and use the
factored-out quote option parsing function.
Escape the closing quote character when quoting indentifiers
Fix handling of quoted names in Parser::SQLite
Fix handling of quoted names in Parser::MySQL
Fix handling of quoted names in Parser::PostgreSQL
Test table and field names with quote characters in them
Fix handling of quoted literals in Parser::SQLServer
Escape the quote charcter when quoting identifiers in Producer::Oracle
Fix handling of quoted names in Parser::Oracle
Fix parsing of DROP TABLE in Parser::Oracle

The grammar is still severely lacking, but at least now it passes
t/60roundtrip.t with a trivial table (no auto-increment or foreign
keys).
Fix escaping/parsing of single-quoted strings in SQLite

Also fix parsing of decimal numbers.
Fix decimal and single-quoted values in Parser::PostgreSQL
Escape single quotes in string default values
Fix handling of escaped quote characters and numeric literals in MySQL
Quote table names in 'SHOW CREATE TABLE' in Parser::DBI::MySQL