PdfWriter.set_need_appearances_writer() (whether called directly or indirectly by PdfWriter.update_page_form_field_values()) fails to create the /Root/AcroForm object correctly when it doesn't already exist in the PdfWriter object.

See #355 (comment) for more details.

Fixes #355

…#1697)

Without this, the logging module logs another error:

    TypeError: not all arguments converted during string formatting

Closes #1689

ContentStream must be stored as individual objects

Fixes  #1654

Created a new _text_extraction submodule. By now most of the text extraction logic is still in `_page.py`, but that should change in future.

Bug Fixes (BUG)
-  compress_content_stream not readable in Adobe Acrobat (#1698)
-  Pass logging parameters correctly in set_need_appearances_writer (#1697)
-  Write /Root/AcroForm in set_need_appearances_writer (#1639)

Robustness (ROB)
-  Allow more whitespaces within linearized file (#1701)