Feature: Add ETF profile scraping, chart data queries, and real-time quotes

[Alfystar]

Hi! First of all, thank you for providing such a solid and well-structured foundation with this library. It has been incredibly useful.

I'm working on a personal project (LibreFolio) and I needed to extend the scraping capabilities to fetch more detailed information about ETFs. I've implemented these features and updated the README accordingly to document them.

Changes & New Features:

• ETF Profile Scraping: Added get_etf_overview to fetch comprehensive data including description, fund size, TER, full country/sector allocations, and top 10 holdings with ISINs.
• Chart Data: Added query_chart and load_chart to retrieve historical performance data and raw JSON responses.
• Real-time Quotes: Added get_gettex_quote to fetch real-time bid/ask data from Gettex.
• Fixes:
  • Refactored boolean column conversion to fix a FutureWarning regarding downcasting behavior in replace.
  • Fixed variable naming for the latest quote date in charts.py.
• Documentation: Updated README.md with usage examples for the new functions and added installation instructions for pipenv.

I hope these additions can be useful to others as well. Feel free to modify the README or the code if it doesn't fully align with your vision for the project.

Thanks again!