Improve mapping of SQL integer types to C corresponding types

[mloskot]

• Fine-grained mapping of SQL integer types to C corresponding types
• Add reading of missing C data types for integers
• Distinguish SQL_C_BIT data type for reading
• Prefer mapping of SQL_C_* types to fixed-width integer types
• Ensure SQL_C_SHORT and SQL_C_LONG are mapped to fixed-width variant types
• Refine reading of SQL_C_TINYINT into int8_t instead of int16_t
• Refine reading of SQL_C_BIT into int8_t
• Make auto-binding of numeric columns signedness-aware

References

Closes #369