Implement Index

[kawasin73]

• [x] sqlite_schema index support #8
  • CREATE INDEX sql syntax : https://www.sqlite.org/lang_createindex.html
• [x] Single integer column index with WHERE <index_column> = <integer>
• [x] Type Conversions Prior To Comparison #7
  • https://www.sqlite.org/datatype3.html#type_conversions_prior_to_comparison
• [x] Collating Sequences for string comparison #23
  • https://www.sqlite.org/datatype3.html#collating_sequences
• [x] Multiple columns index
• [ ] autoindex from PRIMARY KEY support
• [ ] ORDER BY with index support