Added
- Add stitching of statements to produce a single statement across multiple filings
- Add `Statement` class to represent a single statement and `Statements` class to represent multiple statements
- Add `XBRLS` class to combine data from multiple periods with intelligent handling of concept changes
- Add `XBRLS.from_filings` to create a `XBRLS` object from a list of filings
- Add `XBRLS.statements` property to get the statements from the `XBRLS` object