Pdftext

- Use line breaks from pdfium

- Option to keep characters with JSON/dictionary output
- Fix some bugs when interfacing with the pdfium c api (thanks mara004)

- Add probability threshold for block predictions

- Select a range of pages versus converting the whole doc
- Minor internal refactor to use docs versus paths

- Fix bug where hyphens didn't show up at the end of lines
- Improve wrapping for hyphens - join words across hyphens before newline (disable by passing `keep_hyphens`)
- Restructure output to avoid redundant info in json blob - keep track of text spans with similar font info instead of individual characters
- Update model to predict blocks more accurately

- Switch the character box to a `loose` box, to get the full character range