Add strip_url_static_file_prefix to filters
Add strip_url_static_file to base sphinx template and templateexporter.py
Add tests for filter
`strip_files_prefix` now also strips markdown style links, `latex_base` updated to include filter
expand strip_files test coverage
update patterns for strip_files filter

- catch leading '/files' in href/src
- support regular links as well as images in markdown
Merge pull request #4505 from mrmagooey/nbconvert-latex-markdown-images2

files url handling in nbconvert

closes #4191