[MRG] Add error/warning tests

[vinayak-mehta]

#110

• Convert from log to warning
  • "no tables found" in Lattice extract_tables and Stream extract_tables, _generate_columns_and_rows
  • "does not lie in column range" in utils.get_table_index

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• E: Unknown flavor in read_pdf
• E: Input validation utils.validate_input
• E: Unsupported file formats in PDFHandler
• E: Check for no lines found in Lattice _generate_table
• E: Check for length of table_area and columns in Stream
• W: No tables found