Ensure identifiers start with alphabetical character
Rename parse_variable_name -> parse_column_name
Add DB value parsers and condition parser placeholder
Fix number parser, basic condition parser
Move select parser to select module
Add create statement parser
Move condition parser to common; add delete statement parser
Add drop statement parser
Add insert parser
Add update parser, combine operation parsers into one
Add initial validation, fix compiler warnings
Validation WIP
Allow more spaces in create statement, update TableSchema struct
Add create index parser and validator
Add todo in parse_identifier
Rework the new structure, many other changes
